U.S. patent application number 14/176792 was filed with the patent office on 2015-08-13 for apparatus and method for forming three-dimensional objects from solidifiable paste.
This patent application is currently assigned to Global Filtration Systems, a dba of Gulf Filtration Systems Inc.. The applicant listed for this patent is Global Filtration Systems, a dba of Gulf Filtration Systems Inc.. Invention is credited to Ali El-Siblani.
Application Number | 20150224710 14/176792 |
Document ID | / |
Family ID | 53774160 |
Filed Date | 2015-08-13 |
United States Patent
Application |
20150224710 |
Kind Code |
A1 |
El-Siblani; Ali |
August 13, 2015 |
APPARATUS AND METHOD FOR FORMING THREE-DIMENSIONAL OBJECTS FROM
SOLIDIFIABLE PASTE
Abstract
An apparatus and method for making a three-dimensional object
from a solidifiable paste is shown and described. The apparatus
includes a pastes spreader, at least a portion of which extends
into the solidifiable paste. The container holding the solidifiable
paste and the spreader are movable relative to one another. In one
system, the spreader vibrates as the container and the spreader
move relative to one another. In another system, the spreader is
part of a spreader assembly in which a first spreader and second
spreader are angled with respect to one another, and the assembly
is rotatable and lockable into multiple rotational positions. The
apparatus and method allow three-dimensional objects to be
progressively built upside down by ensuring that the previously
solidified object section has a substantially homogeneous layer of
solidifiable material available for forming a new layer of the
solidified object prior to exposure to solidification energy.
Inventors: |
El-Siblani; Ali; (Dearborn
Heights, MI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Global Filtration Systems, a dba of Gulf Filtration Systems
Inc. |
Dearborn Heights |
MI |
US |
|
|
Assignee: |
Global Filtration Systems, a dba of
Gulf Filtration Systems Inc.
Dearborn Heights
MI
|
Family ID: |
53774160 |
Appl. No.: |
14/176792 |
Filed: |
February 10, 2014 |
Current U.S.
Class: |
264/401 ;
425/150 |
Current CPC
Class: |
B33Y 10/00 20141201;
B33Y 70/00 20141201; B29C 64/135 20170801; B33Y 30/00 20141201;
B29K 2105/16 20130101; B29C 64/40 20170801; B29C 64/214 20170801;
B29C 64/241 20170801; B29L 2009/00 20130101; B29C 64/209
20170801 |
International
Class: |
B29C 67/00 20060101
B29C067/00 |
Claims
1. An apparatus for making a three-dimensional object, comprising:
a source of solidification energy; a solidifiable paste container
comprising an open top and a closed bottom and containing a
solidifiable paste that solidifies in response to solidification
energy supplied by the source of solidification energy; a build
platform, wherein the solidifiable paste container is located
between the source of solidification energy and the build platform,
and during an object building process, the build platform moves
along a build axis away from the bottom of the solidifiable paste
container to progressively build the three-dimensional object along
the build axis.
2. The apparatus of claim 1, further comprising a paste spreader,
wherein the paste spreader has a length along a first axis and a
height perpendicular to the length.
3. The apparatus of claim 2, wherein the paste spreader is movable
along a second axis that is perpendicular to the first axis.
4. The apparatus of claim 3, wherein the paste spreader is
vibratable as it moves along the second axis.
5. The apparatus of claim 2, wherein the paste spreader is a first
paste spreader, the apparatus further comprises a second paste
spreader, and the second paste spreader has a length along the
first axis and a height perpendicular to the length.
6. The apparatus of claim 5, wherein the first paste spreader and
the second paste spreader have a fixed angular orientation relative
to one another when viewed along the first axis.
7. The apparatus of claim 5, further comprising a paste spreader
assembly comprising the first paste spreader and the second paste
spreader, wherein the paste spreader assembly is rotatable about an
axis of rotation parallel to the first axis.
8. The apparatus of claim 7, further comprising a lock, wherein the
lock releasably secures the paste spreader assembly in a select one
of a plurality of rotational positions about the axis of
rotation.
9. The apparatus of claim 8, wherein the plurality of rotational
positions is two rotational positions.
10. The apparatus of claim 9, wherein in the first rotational
position, a height dimension of the first paste spreader is
oriented perpendicularly to the closed bottom of the solidifiable
paste container and a height dimension of the second paste spreader
is oriented at an angle relative to the closed bottom of the
solidifiable paste container.
11. The apparatus of claim 8, wherein during a paste spreading
operation, the first paste spreader engages a wall of the
solidifiable paste container or at least one hard stop to adjust
the rotational position of the paste spreader assembly from a first
rotational position about the axis of rotation to a second
rotational position about the axis of rotation.
12. The apparatus of claim 5, wherein the first and second paste
spreaders each have serrated leading edges.
13. The apparatus of claim 2, wherein the solidifiable paste
container is rotatable in a plane perpendicular to the build
axis
14. The apparatus of claim 13, wherein the paste spreader is
vibratable as the container rotates in the plane perpendicular to
the build axis.
15. The apparatus of claim 2, wherein the solidifiable paste
container has a circular cross-section perpendicular to the build
axis.
16. The apparatus of claim 2, wherein the paste spreader has a
leading edge, the leading edge extends beneath the open top of the
solidifiable paste container, and the leading edge has a plurality
of gaps along the first axis.
17. The apparatus of claim 2, wherein the paste spreader is
pivotable to a selected pivot angle about a pivot axis parallel to
the first axis.
18. A method of making a three-dimensional object from a
solidifiable paste, comprising: providing a solidifiable paste
container having an open top, a closed bottom, and containing a
volume of solidifiable paste, wherein the solidifiable paste has an
exposed surface; positioning an exposed surface of a previously
formed section of the three-dimensional object at a distance from
the closed bottom corresponding to a desired layer thickness of the
solidifiable paste; supplying solidification energy to solidify a
portion of the layer thickness of the solidifiable paste in a
pattern corresponding to the three-dimensional object, thereby
forming a newly formed section of the three-dimensional object
having an exposed surface; moving the exposed surface of the newly
formed section of the three-dimensional object along a build axis
away from the closed bottom of the solidifiable paste
container.
19. The method of claim 18, wherein the step of moving the exposed
surface of the newly formed section of the three-dimensional object
along the build axis creates depleted regions of solidifiable paste
within a distance corresponding to the desired layer thickness from
the closed bottom of the solidifiable paste container, and the
method further comprises replenishing the depleted regions with a
portion of the volume of the solidifiable paste without adding
fresh solidifiable paste to the solidifiable paste container.
20. The method of claim 18, further comprising the steps of:
providing a paste spreader, wherein the paste spreader has a length
along a first axis, a height perpendicular to the length, and a
leading edge along the first axis; positioning the leading edge of
the paste spreader beneath the exposed surface of the solidifiable
paste; and moving at least one of the paste spreader and the
solidifiable paste container relative to the other of the paste
spreader and the solidifiable paste container to spread the
solidifiable paste.
21. The method of claim 20, wherein the step of moving at least one
of the paste spreader and the solidifiable paste container relative
to the other of the paste spreader and the solidifiable paste
container is carried out only when an area of the exposed surface
of the three-dimensional object perpendicular to the build (z) axis
intersects of overlaps with an area of solidifiable paste in the
solidifiable paste container used to form a next layer of the
three-dimensional object, where in the area of solidifiable paste
is perpendicular to the build (z) axis.
22. The method of claim 20, wherein the step of moving at least one
of the paste spreader and the solidifiable paste container relative
to the other of the paste spreader and the solidifiable paste
container comprises rotating the solidifiable paste container.
23. The method of claim 20, wherein the step of moving the paste
spreader and the solidifiable paste container relative to one
another comprises traversing the paste spreader along a second axis
perpendicular to the first axis.
24. The method of claim 20, further comprising vibrating the paste
spreader along the build axis while moving the spreader and the
solidifiable paste container relative to one another.
25. The method of claim 20, wherein the spreader leading edge has a
plurality of gaps along the first axis.
26. The method of claim 20, wherein the step of moving at least one
of the spreader and the solidifiable paste container relative to
one another further comprises imparting a textured profile on the
exposed surface of the solidifiable paste.
27. The method of claim 20, wherein the spreader is a first
spreader, and the method further comprises: providing a second
spreader having a length along the first axis, a height
perpendicular to the length, and a leading edge; positioning the
leading edge of the second spreader beneath the exposed surface of
the paste; and moving at least one of the second spreader and the
solidifiable paste container relative to the other of the second
spreader and the solidifiable paste container.
28. The method of claim 27, wherein the step of moving at least one
of the first spreader and the solidifiable paste container relative
to the other of the first spreader and the solidifiable paste
container comprises orienting the height dimension of the first
spreader perpendicularly to the closed bottom of the solidifiable
material container and moving the first spreader and the second
spreader in a first direction along a second axis such that the
first spreader is spaced apart from the second spreader in a second
direction along the second axis, and the step of moving one of the
second spreader and the solidifiable paste container relative to
the other of the second spreader and the solidifiable paste
container comprises orienting the height dimension of the second
spreader perpendicularly to the closed bottom of the solidifiable
material container and moving the first spreader and the second
spreader in the second direction along the second axis such that
the second spreader is spaced apart from the first spreader in the
first direction along the second axis.
29. The method of claim 28, wherein the step of orienting the
height dimension of the second spreader perpendicularly to the
closed bottom of the solidifiable material container comprises
engaging the second spreader with a wall of the solidifiable
material container
30. The method of claim 28, wherein during the step of moving the
first spreader and the second spreader in the first direction along
the second axis, the second spreader is oriented at an angle
relative to the closed bottom of the solidifiable material
container such that the leading edge of the first spreader is
spaced apart from the closed bottom of the solidifiable container
by a first distance along the build axis, the leading edge of the
second spreader is spaced apart from the closed bottom of the
solidifiable container by a second distance along the build axis,
and the first distance is less than the second distance.
31. The method of claim 28, wherein the step of orienting the first
spreader height dimension perpendicularly to the closed bottom of
the solidifiable material container comprises rotating the first
spreader to a first rotational position about an axis of rotation
parallel to the first axis and releasably locking the first
spreader in the first rotational position.
32. The method of claim 31, wherein the step of orienting the
second spreader height dimension perpendicularly to the closed
bottom of the solidifiable material container comprises rotating
the first spreader to a second rotational position about the axis
of rotation and releasably locking the first spreader in the second
rotational position.
33. The method of claim 28, wherein the step of moving at least one
of the spreader and the solidifiable paste container relative to
the other of the spreader and the solidifiable paste container
comprises rotating the solidifiable paste container by at least 180
degrees.
34. An apparatus for supplying a solidifiable paste that solidifies
when exposed to solidification energy, the apparatus comprising: a
solidifiable paste container comprising an open top and a closed
bottom, wherein the container has a height, a cross-sectional area
perpendicular to the height, and an interior volume for holding the
solidifiable paste; a spreader having a length defining a first
axis, wherein the length of the spreader is located within the
cross-sectional area, at least a portion of the spreader extends
into the interior volume, and at least one of the spreader and the
solidifiable paste container is movable relative to the other of
the spreader and the solidifiable paste container while the portion
of the spreader extends into the interior volume.
35. The apparatus of claim 34, wherein the container has walls
defining the open top, the spreader has ends spaced apart from one
another along the first axis, and the ends are spaced apart from
the container walls along the first axis.
36. The apparatus of claim 34, wherein the spreader is pivotable
about a pivot axis parallel to the first axis to a selected angle
relative to the container.
37. The apparatus of claim 34, wherein the spreader is a blade
having a leading edge, the leading edge extends into the interior
volume, and the leading edge has a plurality of gaps along the
first axis.
38. The apparatus of claim 34, wherein the spreader is a blade
having a leading edge and the leading edge is spaced apart from the
closed bottom of the container by an adjustable distance.
39. The apparatus of claim 34, wherein the spreader is vibratable
while the spreader and the solidifiable paste container move
relative to one another.
40. The apparatus of claim 34, wherein the spreader is translatable
relative to the solidifiable paste container across the
cross-sectional area.
41. The apparatus of claim 34, wherein the solidifiable paste
container is rotatable relative to the spreader.
42. The apparatus of claim 41, wherein the solidifiable paste
container is rotatable by at least about 180 degrees.
43. The apparatus of claim 34, wherein the spreader is a first
spreader, the apparatus further comprises a second spreader, the
second spreader has a length along the first axis, at least a
portion of the second spreader extends into the interior volume,
and at least one of the second spreader and the solidifiable paste
container is movable relative to the other of the second spreader
and the solidifiable paste container while the at least a portion
of the second spreader extends into the interior volume.
44. The apparatus of claim 43, wherein the first spreader and the
second spreader have a fixed angular orientation relative to one
another when viewed along the first axis.
45. The apparatus of claim 43, further comprising a spreader
assembly comprising the first spreader and the second spreader,
wherein the spreader assembly is rotatable about an axis of
rotation parallel to the first axis.
46. The apparatus of claim 45, further comprising a lock, wherein
the lock releasably secures the spreader assembly in a select one
of a plurality of rotational positions about the axis of
rotation.
47. The apparatus of claim 46, wherein in a first rotational
position, a height dimension of the first spreader is oriented
perpendicularly to the closed bottom of the solidifiable paste
container and a height dimension of the second spreader is oriented
at an angle relative to the closed bottom of the build
platform.
48. The apparatus of claim 46, wherein during a paste spreading
operation, the first spreader engages a wall of the solidifiable
paste container or at least one hard stop to adjust the rotational
position of the spreader assembly from a first rotational position
about the axis of rotation to a second rotational position about
the axis of rotation.
49. The apparatus of claim 43, wherein the first and second
spreaders each have serrated leading edges.
50. The apparatus of claim 34, wherein the cross-sectional area is
circular.
51. The apparatus of claim 34, wherein the cross-sectional area is
rectangular.
52. The apparatus of claim 34, wherein the closed bottom of the
solidifiable paste container is transparent and/or translucent.
53. The apparatus of claim 34, wherein the extent to which the
spreader extends into the interior volume defines a depth of
penetration into the interior volume, and the depth of penetration
is adjustable.
54. The apparatus of claim 34, further comprising a motor
operatively connected to the spreader such that when the motor is
energized, the spreader moves relative to the container along a
second axis, and a controller programmed to selectively energize
the motor.
Description
FIELD
[0001] The disclosure relates to an apparatus and method for
manufacturing three-dimensional objects, and more specifically, to
an apparatus and method for manufacturing such objects from a
solidifiable paste.
DESCRIPTION OF THE RELATED ART
[0002] Three-dimensional rapid prototyping and manufacturing allows
for quick and accurate production of components at high accuracy.
Machining steps may be reduced or eliminated using such techniques
and certain components may be functionally equivalent to their
regular production counterparts depending on the materials used for
production.
[0003] The components produced may range in size from small to
large parts. The manufacture of parts may be based on various
technologies that solidifying solidifiable materials into a
hardened three-dimensional object. Certain technologies use
photo-polymer hardening using light or laser curing methods.
Secondary curing may take place with exposure to, for example,
ultraviolet (UV) light. A process to convert a computer aided
design (CAD) data to a data model suitable for rapid manufacturing
may be used to produce data suitable for constructing the
component. Then, a pattern generator may be used to construct the
part. An example of a pattern generator may include the use of DLP
(Digital Light Processing technology) from Texas Instruments.RTM.,
SXRD.TM. (Silicon X-tal Reflective Display), LCD (Liquid Crystal
Display), LCOS (Liquid Crystal on Silicon), DMD (digital mirror
device), J-ILA from JVC, SLM (Spatial light modulator) or any type
of selective light modulation system. One technique that may be
used to form a three-dimensional object involves the use of a
linear solidification device.
[0004] In certain applications, it is desirable to form
three-dimensional objects from a solidifiable paste, such as a
highly viscous resin, a semi-solid, a gel, or a blend of such
materials with wax, or metal, or ceramic fillers. Such applications
include the formation of dental appliances such as arches, crowns,
or orthodontic appliances. Unlike low or medium viscosity
materials, solidifiable pastes typically do not flow due to the
force of gravity alone. Thus, when a layer of the paste is
solidified, it creates a depleted area of solidifiable paste. If
some means is not provided for replenishing the depleted paste,
insufficient paste may be available to form the next or subsequent
object layers. In certain investment casting processes, a
solidifiable paste is provided which comprises a wax filler and a
polymeric binder. However, in known processes of solidifying such
solidifiable pastes, the amount of wax in the solidifiable paste
has been limited to no greater than 25 percent because of the
inability to replenish the depleted paste. In general, it is
preferable to increase the amount of wax filler for easier casting.
Thus, this limit is generally undesirable.
[0005] The problem of replenishing depleted areas of solidifiable
paste may be particularly acute when using "upside down" build
processes. Certain method of manufacturing three-dimensional
objects have been developed wherein a build platform descends as a
three-dimensional object is progressively built upward in a
direction away from the build platform. These processes may be
termed "right-side up" processes because the orientation of the
object during the build process is the same as the orientation of
the finished object when in use. In right-side up processes,
synergistic stimulation to convert the solidifiable paste to a
three-dimensional object is generally applied in a downward
direction onto the exposed surface of the solidifiable paste. In
certain known "right-side up" build processes, the solidifiable
object is progressively immersed into the paste during
solidification. In order to provide a homogeneous layer of paste to
solidify an object layer, the build platform may be dropped by an
amount greater than the layer thickness and then brought upward.
This action tends to break up bubbles and replenish depleted areas
of solidifiable paste.
[0006] "Upside down" build processes differ from "right-side up"
processes in that a build platform is suspended upside down and
progressively moves upward as the three-dimensional object is
progressively built in a downward direction. These types of methods
may be termed "upside down" processes because during the object
building process the object is oriented upside down relative to the
orientation of the finished object as designed and when in use. In
certain known upside down processes, a volume of solidifiable
material is provided in a tray or basin with a closed bottom.
During the formation of each object layer, the build platform is
positioned so that the exposed (downward facing) surface of the
last formed object layer is spaced apart from the bottom of the
closed tray by a desired layer thickness. In the case of low or
medium viscosity liquids, this typically does not present a problem
because the action of gravity will cause the volume of solidifiable
material to flow into regions that were previously depleted due to
the formation of solidified object sections, thus providing a
homogeneous volume of solidifiable material for the next layer
formation step. However, this is not the case with solidifiable
pastes. Known upside down build processes are not configured to
replenish depleted solidified paste regions in a volume of
solidifiable paste. As a result, a need has arisen for an apparatus
and method that addresses the foregoing concerns.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] The disclosure will now be described, by way of example,
with reference to the accompanying drawings, in which:
[0008] FIG. 1 is a side elevation view of an apparatus for making a
three-dimensional object in an upside down build process used with
low or medium viscosity solidifiable materials;
[0009] FIG. 2 is a front elevational view of an apparatus for
making a three-dimensional object from a solidifiable paste in an
upside down build process, wherein the apparatus includes a first
exemplary paste spreader assembly;
[0010] FIG. 3 is a side elevational view of the apparatus of FIG.
2;
[0011] FIG. 4 is a top plan view of an apparatus for making a
three-dimensional object from a solidifiable paste in an upside
down build process, wherein the apparatus includes a second
exemplary paste spreader assembly;
[0012] FIG. 5 is a front elevational view of the apparatus of FIG.
4;
[0013] FIG. 6 is a perspective view of an apparatus for making a
three-dimensional object from a solidifiable paste in an upside
down build process, wherein the apparatus includes a third
exemplary paste spreader assembly with the first and second
spreaders in a first rotational orientation;
[0014] FIG. 7 is a perspective view of the apparatus of claim 7
with the first and second spreaders in a second rotational
orientation;
[0015] FIG. 8A is a close-up view of a portion of the paste
spreader assembly of FIG. 6 with the first and second spreaders in
the first rotational orientation of FIG. 6 showing the first
spreader approaching abutting engagement with an inner wall of the
solidifiable paste container assembly during a first paste
spreading operation;
[0016] FIG. 8B is a close-up view of the portion of the paste
spreader assembly of FIG. 8A with the first and second spreaders in
a third rotational orientation and the first spreader in abutting
engagement with the inner wall of the solidifiable paste container
following a first paste spreading operation and before initiating a
second paste spreading operation;
[0017] FIG. 9 is a close-up perspective view of a portion of the
paste spreader assembly of FIG. 6 showing the spreader assembly
motor, first and second spreader blades, carriage, and rotational
lock;
[0018] FIG. 10 is a close-up perspective view of a portion of the
paste spreader assembly of FIG. 6 showing the carriage removed and
the engagement of the rack gear with the spreader assembly motor
pinion gear;
[0019] FIG. 11 is a flow chart illustrating a first exemplary
method of making a three-dimensional object from a solidifiable
paste;
[0020] FIG. 12 is a flow chart depicting an exemplary set of steps
for the step of moving the paste spreader relative to the
solidifiable paste container or vice-versa in FIG. 11; and
[0021] FIG. 13 is a flow chart depicting a second exemplary method
of making a three-dimensional object from a solidifiable paste.
[0022] Like numerals refer to like parts in the drawings.
DETAILED DESCRIPTION
[0023] The Figures illustrate examples of an apparatus and method
for manufacturing a three-dimensional object from a solidifiable
paste. Based on the foregoing, it is to be generally understood
that the nomenclature used herein is simply for convenience and the
terms used to describe the invention should be given the broadest
meaning by one of ordinary skill in the art.
[0024] The apparatuses and methods described herein are generally
applicable to additive manufacturing of three-dimensional objects,
such as components or parts (discussed herein generally as
objects), from a solidifiable paste. As used herein, the term
"paste" refers to a thick, viscous material that is spreadable but
which is not deformable under gravity alone. The term "solidifiable
paste" refers to a paste that is transformable from a spreadable
state to a hardened, non-spreadable state due to the application of
solidification energy such as electromagnetic radiation. In certain
preferred examples, the solidifiable pastes described herein are
photohardenable compositions that solidify in response to invisible
or visible light. The photohardenable compositions typically
include a photoinitiator that initiates polymerization and/or
cross-linking in response to electromagnetic radiation of a
particular wavelength or range of wavelengths. Certain
photoinitiators are "free radical" initiators that generate free
radicals to initiate the polymerization and/or cross-linking
process. Other photoinitiators are "cationic" photoinitiators that
generate cations to initiate the polymerization and/or
cross-linking process.
[0025] The solidifiable pastes described herein are preferably
highly viscous and have a viscosity of at least about 10,000
centipoise (cp), preferably at least about 15,000 cp, more
preferably at least about 20,000 cp, still more preferably at least
about 50,000 cp, even more preferably at least about 60,000 cp,
more preferably at least about 70,000 cp, yet more preferably at
least about 80,000 cp, even more preferably at least about 90,000
cp, and still more preferably at least about 100,000 cp. In certain
examples, the solidifiable pastes described herein have viscosities
of at least about 150,000 cp, at least about 200,000 cp, at least
about 300,000 cp, at least about 400,000 cp, at least about 500,000
cp, at least about 600,000 cp, at least about 700,000 cp, at least
about 800,000 cp, at least about 900,000 cp, at least about
1,000,000 cp, or at least about 2,000,000 cp. At the same time, the
solidifiable pastes described herein preferably have a viscosity
that is no greater than about 100,000,000 cp, no greater than about
90,000,000 cp, no greater than about 80,000,000 cp, no greater than
about 70,000,000 cp, no greater than about 60,000,000 cp, no
greater than about 50,000,000 cp, no greater than about 40,000,000
cp, no greater than about 30,000,000 cp, no greater than about
20,000,000 cp, or no greater than about 10,000,000 cp.
[0026] The solidifiable pastes described herein may comprise a gel,
a cream, a glue, an adhesive, and/or a semi-solid. The solidifiable
pastes may comprise polymeric components and non-polymeric
components. The polymeric component may comprise a binder with or
without fillers. Suitable binders include polymers, copolymers,
terpolymers, block copolymer, or blends of any of the foregoing.
The binder may be uncross-linked or partially cross-linked.
Accordingly, suitable polymers for the binder component include,
but are not limited to: acrylate and/or methacrylate containing
compounds, for example mono-, di-, tri-, tetra-, pentacrylate, such
as alkyl- or alkoxy-(meth)acrylates, (meth)acrylic esters having
short or long chain alkyl ester groups, e.g. alkyl glycol
di(meth)acrylate; epoxy group containing compounds; vinyl group
containing or vinyl ether group containing compounds;
polysiloxanes; and the like, as well as mixtures thereof.
Alternatively, a thermal hardening polymer substance such as an
epoxy group containing compound may be used, which is preferably
protected with an amine group that decomposes in response to light
and/or heat. At least a portion of the polymeric component is
solidifiable in response to appropriate synergistic stimulation,
such as electromagnetic radiation of a wavelength suitable to
initiate polymerization and/or cross-linking. However, the
polymeric component may also include crosslinked or un-crosslinked
polymers as fillers that do not further polymerize or cross-link in
response to the applied synergistic stimulation.
[0027] The binder may also include non-polymeric, auxiliary agents
used to facilitate polymerization and/or cross-linking, including
but not limited to: photoinitiators, which may be selected
depending on the desired wavelength of electromagnetic and/or
synergistic radiation, such as
2-benzyl-2-dimethylamino-1(4-morpholino phenyl)butanone,
1,2,2'-dimethoxy-2-phenylacetophenol, bisimidazoles, benzophenones,
.alpha.-aminoketones, xanthenes, fluorenes, fluorones, ferrocenes,
and the like; co-initiators and/or activation agents such as
thioxanthones (e.g. isopropyl
thioxanthonel-chloro-4-propoxythioxanthone),
4-benzoyl-4'-methyldiphenyl sulfide, ethyl-p-dimethylaminobenzoate,
N,N-dialkyl-toluidine or -aniline, benzophenones, diaryliodo
compounds, borates, phosphites, and the like
[0028] A filler which may be mixed with a binder for providing a
solidifiable paste typically is a solid or substantially solid
substance and may include, without being limited to: a ceramic
substance such as e.g. alumina, magnesia, zirconia, ceramic oxides
of other transition metals such as titania, hafnium oxide, rare
earth metal oxides, spinel type double metal oxide ceramics, or
mixtures thereof; cermets; silicate, aluminosilicate, apatite,
fluoroapatite, hydroxylapatite, phosphates such as tricalcium
phosphate, calcium magnesium phosphate, calcium ammonium phosphate,
mullite, spinels, and mixtures thereof; glass materials, such as
silicate glass, borsilicate glass, quartz glass and mixtures
thereof; carbon black; pigments; metals and metal alloys such as
stainless steel, titanium or titanium alloy, nickel alloy, copper
or copper alloy such as brass (70% copper and 30% zinc), aluminum
or aluminum alloy, iron or iron alloy and mixtures thereof; solid
polymers or polymer blends such as polymerized acrylic resins and
blends or copolymers thereof like polyurethane/polyacrylates,
acrylonitrile/butadiene/styrene-polymerisates (ABS), epoxides and
copolymers thereof, nylon and blends or copolymers thereof,
polyamid elatomers and mixtures thereof, and other filler
substances, including waxes.
[0029] Ceramic fillers are particularly beneficial for dental
applications in terms of achieving high mechanical strength at good
homogeneity combined with high size accuracy (especially when the
process includes post-treatment such as sintering and thereby a
transformation from a first to a second circumferential size).
Exemplary ceramic fillers include powders comprising ceramic
materials selected from alumina, zirconia, or a mixture thereof. A
particularly preferred ceramic powder comprises a ceramic material
selected from monoclinical or non-monoclinical zirconia,
yttria-doped or -stabilized tetragonal monoclinical or
non-monoclinical, single or non-single phased zirkonia (i.e. ZrO2
containing 3-5 mol-% Y.sub.2O.sub.3), especially 3YTZP.
[0030] The filler component may further comprise one or more kinds
of additives, for example but not limited to dispersants, coloring
agents such as pigments, post-treatment auxiliary additives such as
sintering aids or stabilizers, etc. The filler may co-fuse or
co-sinter itself under the action of electromagnetic radiation
and/or synergistic stimulation used for solidification (e.g.
especially when polymer fillers are used). It is on the other hand
preferred that the filler itself is inert with respect
electromagnetic radiation and/or synergistic stimulation at a level
which solidifies the binder admixed with the filler, but may
nevertheless co-fuse or co-sinter in a post-treatment described
later (e.g. when ceramics, glass or metals/metal alloys are
used).
[0031] The filler may be in the form of particles, a powder,
fibers, a net, a scaffold, and the like. The particularly preferred
particulate form of the filler is a powder having a suitable
particle size, preferably being spherical or essentially spherical
in shape, and further preferably having a mean particle size in a
range of about 0.001 microns to 100 microns, more preferably in a
range of about 0.01 to 50 microns and particularly in a range of
about 0.1 to 10 microns. As to the distribution of the absolute
particle size of the filler, it may range from about 1 nm to 1000
microns or higher, more preferably from about 0.1 microns to 100
microns. The filler may have a monomodal, a bimodal or a trimodal
size distribution, using the same or different filler materials.
Solidifiable pastes described herein may also include rheology
adjusting agents, viscosity adjusting agents, diluents, solvents,
colorants such as dyes and/or color pigments, thixotropic agents,
thickeners, stabilizers, coupling agents, wetting agents,
dispersants, lubricants, adhesives, pore forming agents, and the
like, respectively alone or in combination.
[0032] In certain preferred examples, the solidifiable pastes
described herein are used for investment casting and comprise a wax
powder filler with a polymeric binder that solidifies in response
to solidification energy. The amount of wax by weight of the
solidifiable paste is preferably greater than 25 percent, more
preferably at least about 30 percent, still more preferably at
least about 40 percent, and even more preferably, at least about 50
percent. In certain preferred examples, the solidifiable paste
comprises a wax powder and a polymeric binder, and the percentage
by weight of solidifiable paste of the wax powder is from about 50
percent to about 60 percent. In one example of a solidifiable paste
comprising a wax powder and a polymeric binder, a Microease 114S
synthetic wax powder supplied by Micro Powders, Inc. of Tarrytown,
N.Y. is combined with a PIC 100 Photopolymer supplied by
Envisiontec, Inc. of Dearborn, Mich. to form a paste comprising 50
to 60 percent by weight of the Microease 114S and 40 to 50 percent
by weight of the PIC100 photopolymer. In another example, the
Microease 114S is combined with a EC500 photopolymer supplied by
Envisiontec to form a solidifiable paste comprising 50 to 60
percent by weight of the Microease 114S and 40 to 50 percent by
weight of the EC500. In another example of a solidifiable paste
comprising 50 percent by weight of the Microease 114S and 50
percent by weight of PIC100, the solidifiable paste has a resulting
viscosity of from about 1,000,000 cp to about 2,000,000 cp.
[0033] In accordance with a first example of an apparatus for
making a three-dimensional object from a solidifiable paste, the
apparatus comprises a source of solidification energy, a
solidifiable paste container, and a build platform. The
solidifiable paste container has an open top and a closed bottom
and contains a solidifiable paste that solidifies in response to
solidification energy provided by the source of solidification
energy. The solidifiable paste container is located between the
source of solidification energy and the build platform. During an
object building process, the build platform moves along a build
axis away from the solidifiable paste container to progressively
build the three-dimensional object along the build axis. In certain
implementations, the apparatus includes a solidifiable paste
spreader, which may be provided as part of a paste spreader
assembly.
[0034] FIG. 1 illustrates a system 40 for making a
three-dimensional object using low or medium viscosity solidifiable
materials other than solidifiable pastes. The system 40 is an
"upside-down" system in which three-dimensional object 59 is built
upside down. When three-dimensional object 59 is removed from build
platform 44, the build-platform contacting surface 60 of object 59
will be oriented beneath the top surface of the object. The
subsequent figures provide modifications to the basic system of
FIG. 1 which include solidifiable paste spreaders and/or
solidifiable paste spreader assemblies. System 40 includes a
housing 54 used to support a solidifiable material container 48, a
linear solidification device 42, and a build platform 44.
[0035] In the example of FIG. 1, the solidification energy source
is provided in a pattern generator comprising linear solidification
device 42. Linear solidification device 42 scans adjacent linear
patterns of solidification energy along one axis (the y-axis) while
moving along another axis (the x-axis). Suitable linear
solidification devices 42 include a source of solidification energy
and a linear scanning device. In one example, a linear
solidification device 42 includes a laser diode that projects
solidification energy onto a rotating polygonal mirror comprising a
plurality of facets. The rotating polygonal mirror acts as a linear
scanning device. As the solidification energy progressively
traverses the length of a given facet due to the rotation of the
mirror, the facet deflects solidification energy in a linear
pattern along a surface of the solidifiable paste that is in
contact with the closed bottom of solidifiable material container
48. Other suitable linear solidification devices 42 comprise a
laser diode that projects solidification energy to laser scanning
micromirrors such as magnetically-actuated MOEMS
(micro-optical-electromechanical systems). Examples of linear
solidification devices are described in FIGS. 3, 4, and 5A-5D of
Applicant's co-pending U.S. patent application Ser. No. 13/534,638,
filed on Jun. 27, 2012 and the corresponding text, including at
paragraphs 60-79 and 86-104, the contents of which are hereby
incorporated by reference. Pattern generators other than linear
solidification devices may also be used with system 40. Exemplary
pattern generators other than linear solidification devices which
may be used include DLP (Digital Light Processing technology) from
Texas Instruments.RTM., SXRD.TM. (Silicon X-tal Reflective
Display), LCD (Liquid Crystal Display), LCOS (Liquid Crystal on
Silicon), DMD (digital mirror device), J-ILA from JVC, SLM (Spatial
light modulator) or any type of selective light modulation system.
Pattern generators that "draw" laser energy in two-dimensionally
varying patterns across an exposed surface of solidifiable material
may also be used, such as those that comprise a laser in optical
communication with x
[0036] The pattern generator supplies energy patterns that
correspond to object data representative of the three-dimensional
object to the solidifiable material so that the solidifiable
material solidifies in a shape that also corresponds to the object
data. In the case of spatial light modulators, the energy patterns
are typically defined by the ON or OFF states or gray scale or
color values of a plurality of imaging elements that spatially
correspond to different locations on the exposed surface of the
solidifiable material. In the case of linear solidification
devices, the energization state of a solidification energy source
(such as a laser diode) relative to a position and/or other
temporally varying characteristics of a linear scanning device. For
example, with linear solidification devices that are configured as
a laser diode in optical communication with a rotating polygonal
mirror, the pattern of energy supplied to the exposed surface of
the solidifiable material will be determined by the position of the
linear solidification device along a travel axis, the state of the
laser (ON or OFF), and the rotational position of the rotating
polygonal mirror.
[0037] Referring still to FIG. 1, solidifiable material container
48 comprises sidewalls 62 and a bottom that comprises a rigid or
semi rigid solidification substrate 52 that is transparent and/or
translucent with a transparent and/or translucent film 55 coating
adhered to its upper surface. As mentioned previously, the system
of FIG. 1 is preferably used with low or medium viscosity materials
other than solidifiable pastes. During an object forming operation,
the exposed surface 64 of the partially-formed three-dimensional
object 59 is immersed beneath the exposed surface 53 of
solidifiable material 50. Although the spacing is not visible in
FIG. 1, the exposed object surface 64 is preferably immersed such
that it is spaced apart along the build (z) axis from the film 55,
which along with rigid or semi-rigid, transparent and/or
translucent solidification substrate 52 defines the closed-bottom
of the solidifiable material container 48. The z-axis spacing
(.DELTA.z) is the layer thickness of solidifiable material used to
form the next solidified object layer. Once the exposed object
surface 64 is positioned at the desired layer thickness from the
film 55/substrate 52, solidification energy is supplied from a
pattern generator, such as linear solidification device 42. The
solidifiable material within the layer thickness then solidifies in
a pattern that corresponds to the solidification energy pattern
provided by the pattern generator.
[0038] Once the solidified object layer is formed, the exposed
surface 64 of the solidified object 59 will be in contact with film
55. The operation of elevator 58 pulls the build platform 44 upward
to create space for the next object layer. Due to the
solidification process, a portion of the volume of solidifiable
material 50 in solidifiable material container will be depleted. In
the case of low and medium viscosity materials, the remaining
solidifiable material 50 in solidifiable material container 48 will
readily flow into the depleted area to create a homogeneous volume
of solidifiable material 50, which in turn provides an even layer
thickness of solidifiable material between the exposed object
surface 64 and the film 55. However, in the case of solidifiable
pastes, the depleted zones will not be filled because gravity
forces will be insufficient to cause the paste to flow into the
depleted zones.
[0039] FIGS. 2 and 3 depict a first modified version of the system
40 FIG. 1. Unlike the system 40 of FIG. 1, the system of FIGS. 2
and 3 includes a solidifiable paste container 48 and a paste
spreader assembly 84. For ease of illustration, the solidifiable
paste is not shown in FIGS. 2-3. However, a volume of the paste
would be included in the solidifiable paste container 48.
[0040] In the system of FIGS. 2 and 3, solidifiable paste container
48 comprises a rigid or semi-rigid, transparent and/or translucent
solidification substrate 52, a base 70, and a frame assembly
comprising an inner frame 72 and an outer frame 74. Inner frame 72
is generally rigid (e.g., plastic or metal) and comprises four side
walls 76a-76d (wall 76(d) is not shown in FIG. 2 for ease of
viewing) Inner frame 72 also has a horizontal lip 73 that projects
outwardly away from the interior space defined by side walls
76a-76d in a direction parallel to the x-y plane. Outer frame 74 is
also generally rigid (plastic or metal) and comprises four vertical
walls (not labeled for ease of viewing). Inner frame 72 and outer
frame 74 define a frame assembly. In an installed condition, the
horizontal lip 73 of inner frame 72 fits over the top surface of
outer frame 74 to define the upper surface of the frame assembly
and the upper surface of solidification paste container 48. A
plurality of fasteners (not shown) project through horizontal lip
73 and engage corresponding holes (not shown) formed in the upper
surface of outer frame 74 to secure the inner frame 72 to the outer
frame 74. In one example, base 70 is connected to outer frame 74
such as by a plurality of screws or other fasteners. The frame
assembly of FIGS. 2-3 is illustrated in greater detail in FIGS. 5-8
and paragraphs 82-88 of Applicant's co-pending U.S. patent
application Ser. No. 13/361,803, filed Jan. 30, 2012, the contents
of which are hereby incorporated by reference.
[0041] Rigid or semi-rigid, transparent and/or translucent
solidification substrate 52 is connected to base 70 such as by an
adhesive applied around the inner perimeter of base 70 and/or the
outer perimeter of substrate 52. In the example of FIG. 8, the
lower surface of substrate 52 is disposed above the lower surface
of base 70 to prevent damaging substrate 52 when base 70 is placed
on a table or other surface such as during maintenance activities.
Solidification substrate 52 is generally rigid or semi-rigid and
substantially permeable to the energy supplied by linear
solidification device 42 (or whatever type of pattern generator is
provided). In certain examples, it is preferred that the energy
from linear solidification device 42 can pass through
solidification substrate 52 without a significant diminution in
transmitted energy or a significant alteration of the energy
pattern or spectrum transmitted to the solidifiable paste relative
to the pattern and spectrum of the radiation that is incident to
the lower surface of solidification substrate 52. In the case where
the energy provided by linear solidification device 42 or another
kind of pattern generator is a light pattern (including non-visible
light such as UV light), solidification substrate 52 is preferably
substantially transparent and/or translucent to the wavelengths of
light supplied by the linear solidification device 42 or other
pattern generator. As energy is supplied to the surface of the
solidifiable paste that is in contact with solidification substrate
52, the paste will begin to solidify in accordance with the energy
pattern supplied by the linear solidification device 42 or other
type of pattern generator.
[0042] One example of a rigid or semi-rigid solidification
substrate 52 is a transparent and/or translucent float glass.
Another example is a transparent and/or translucent plastic. A
variety of different float glasses and plastics may be used.
Exemplary plastics that may be used include transparent acrylic
plastics supplied by Evonik under the name Acrylite.RTM.. Substrate
52 is preferably rigid enough to provide a substantially planar
surface of solidifiable paste at the substrate 52 when
solidification energy is projected through the substrate 52. The
term "transparent" is meant to indicate that substrate 52 is
capable of transmitting the light wavelengths (including
non-visible light such as UV light if supplied by linear
solidification device 42) necessary to solidify the solidifiable
paste and that neither the intensity of such wavelengths nor the
geometry of the energy pattern is significantly altered as the
light passes through substrate 52. In certain examples, the
solidifiable material container 48 is tiltable relative to object
build platform 44 platform and an object section formed thereon
(e.g., object 59 in FIG. 1) to facilitate peeling of exposed object
surface 64 from rigid or semi-rigid, transparent and/or translucent
solidification substrate 52.
[0043] In certain embodiments, the solidifiable paste may adhere
strongly to the solidification substrate 52 when solidified,
causing the object 59 (FIG. 1) to break or deform when build
platform 44 moves away from linear solidification device 42 along
the build (z) axis during an object building operation. Thus, in
certain examples, a solidification substrate assembly comprising
both a rigid or semi-rigid transparent and/or translucent
solidification substrate and one or more films is provided. In one
example, and as shown in FIG. 8 of U.S. application Ser. No.
13/361,803, a single film is provided adjacent solidification
substrate 52. In some examples, the film is resilient, while in
others a resilient film is not required. Suitable resilient films
include silicone elastomers. One particular example of a suitable
silicone elastomer is Elastosil.RTM. RT 601, which is supplied by
Wacker Silicones. Elastosil.RTM. RT 601 is a transparent,
addition-curing silicone rubber having greater than 88 percent
transmission of light in the 325-700 nm range (for a 10 mm layer).
The material has an elongation at break of about 100 percent (ISO
37), and a tensile strength of about 7.0 N/mm.sup.2 (DIN ISO 37)
tear strength (ASTM D 624B) of about 3.0 N/mm.sup.2. Suitable
non-resilient films include homopolymers or copolymers formed from
ethylenically unsaturated, halogenated monomers, such as
fluoropolymers. Examples of suitable non-resilient films include
polyvinylidene fluoride (PVDF), ethylenchlorotrifluoroethylene
(ECTFE), ethylenetetrafluoroethylene (ETFE),
polytetrafluoroethylene (PTFE), perfluoroalkoxy (PFA), and modified
fluoroalkoxy (a copolymer of tetrafluoroethylene and
perfluoromethylvinylether, also known as MFA). Other suitable films
include PVDF films sold under the Kynar.RTM. name by Arkema, ECTFE
films sold under the Halar.RTM. name by SolvaySolexis, ETFE films
sold under the Tefzel.RTM. name by DuPont, PFA films sold under the
Teflon.RTM.--PFA name by DuPont, and MFA films sold under the name
Nowofol.
[0044] A variety of combinations of films and configurations may be
used to create a suitable solidification substrate assembly. In one
example, a rigid or semi-rigid transparent and/or translucent
solidification substrate is attached to a resilient film, such as a
silicone film. In another example, a rigid or semi-rigid
transparent and/or translucent solidification substrate is attached
to a resilient film which is in turn attached to a non-resilient
film, such as an MFA film. In yet another example, a rigid or
semi-rigid transparent and/or translucent solidification substrate
is attached to a resilient film and a loose non-resilient film is
provided between the resilient film and the rigid or semi-rigid,
transparent and/or translucent solidification substrate.
[0045] As an alternative to the structure depicted in FIG. 2,
solidifiable material container 48 may comprise a basin formed from
polymeric materials. In one example, a basin comprising a
transparent and/or translucent resilient bottom and resilient side
walls is used. In certain implementations, both the transparent
and/or translucent resilient bottom and resilient side walls are
formed from the same or different silicone polymers. In another
implementation, a basin comprising non-resilient acrylic side walls
and a resilient silicone bottom is used. In another example, the
bottom of the basin is defined by a rigid or semi-rigid,
transparent and/or translucent solidification substrate that is
connected to side walls formed of a resilient or plastically
deformable polymeric material. In a further example, the substrate
52 may be coated with a resilient transparent material, such as a
silicone, that extends only a portion of the way to the side walls,
leaving a peripheral gap around the coating and between the coating
and the sidewalls. In yet another example, the substrate 52 may be
coated with a resilient transparent material that extends all the
way to the side walls. In certain examples, a tilting mechanism may
be provided that tilts the solidifiable paste container 48 with
respect to the build platform 44 to peel solidified solidifiable
paste from the bottom of the solidifiable paste container. A
non-resilient material such as a transparent non-resilient film 55
may also be provided as a layer on top of the resilient bottom
between the resilient bottom and the build platform 44.
[0046] In FIGS. 2 and 3 the solidifiable paste container 48 is
secured to the housing 54 (see FIG. 1) by a solidifiable paste
container holder 77 (see FIG. 6). Only a portion of the
solidifiable paste container holder 77 is visible in FIGS. 2 and 3.
Solidifiable paste container holder 77 comprises a lower frame 79
and two locking members 78a and 78b which are spaced apart from one
another along the x-axis. The lower frame 79 comprises two side
walls 80a and 80b. To secure the solidifiable paste container 48 to
housing 54, knobs 82a and 82b are rotated to loosen the locking
members 78a and 78b, which may then be slid upward along sliding
supports (not shown). The base 70 is then inserted along the y-axis
direction so that the sides of base 70 which are spaced apart along
the x-axis may be inserted into the two spaces defined on one side
by the locking member 78a and lower frame sidewall 80a and on the
other side by the locking member 78b and lower frame sidewall 80b.
Once the solidifiable paste container 48 is thusly inserted, the
locking members 78a and 78b may be placed in abutting engagement
with respective sides of the base 70, and the knobs 82a and 82b may
be rotated to lock the base 70 and the container 48 into place.
[0047] Referring again to FIGS. 2 and 3, a build platform assembly
is provided comprising build platform 44, build platform handles
104a and 104b and build platform vertical supports 102a and 102b. A
build platform holder comprising a metal plate 107 with side
grooves 103a and 103b (FIG. 6 shows groove 103b) is fixedly
attached to build platform holder support 46, which is in turn
fixedly attached to build platform elevator 58. The build platform
holder support 46 is movable along the build (z) axis to move the
build platform 44 in first and second directions (up and down)
along the build (z) axis. The build platform assembly is removably
securable to the build platform holder support 46 via engagement
with the side grooves 103a and 103b. A build platform motor (not
shown) is selectively energizable to move build platform holder
support 46 along elevator 58 to move the build platform 44 towards
or way from the solidifiable paste container 48 along the build (z)
axis. In certain examples, a build platform controller is provided
which outputs a signal to the build platform motor to selectively
energize and de-energize the build platform motor as directed by
one or more control programs stored in the controller memory and
executed by the controller processor.
[0048] The system of FIGS. 2 and 3 also includes a paste spreader
assembly 84. The paste spreader assembly 84 comprises a spreader
86, that is mounted to a carriage 90. Following the solidification
of one or more layers of object 59 (FIG. 1), the spreader 86 is
traversed along the x-axis to spread the solidifiable paste and
fill in areas of solidifiable paste that were depleted due to
solidification. A variety of different spreader 86 geometries may
be provided. In certain implementations, the spreader 86 comprises
a single blade with a length along the y-axis direction and a
height along the build (z) axis direction. In other
implementations, and as illustrated in greater detail in FIGS.
6-10, the spreader 86 may comprise two blades, each having a length
along the y-axis and a width perpendicular to the length. In
addition, while the spreader is traversed along the x-axis in the
example of FIGS. 2-3, it may be configured instead to be traversed
along the y-axis. In certain preferred examples, the direction of
traversal corresponds to the smaller dimension of the solidifiable
paste container 48 in the x-y plane.
[0049] In certain examples, a paste spreading operation may be
carried out by traversing the spreader 86 following the
solidification of each layer. However, in other examples, it may
not be necessary to traverse the spreader if the x-y region of
solidifiable paste that is used to form one layer is distinct and
non-overlapping with the x-y region of solidifiable paste used to
form an immediately adjacent layer because the formation of one
layer will not deplete paste from the x-y region used to form the
adjacent layer. Thus, in some preferred examples, a paste spreading
operation is carried out only when the x-y area of the next object
layer to be formed intersects or overlaps with the x-y area of the
previously formed layer.
[0050] In the example of FIGS. 2 and 3, the spreader 86 has a
length along the y-axis and a height perpendicular to the length.
The height dimension may be pivoted to different rotational
orientations in the x-z plane, as described further below. In FIGS.
2 and 3 the height dimension of spreader 86 is parallel to the
build (z) axis. The spreader 86 comprises a shaft or elongated
member 88 that extends along the y-axis and a plurality of blades
89a-89g, each of which has lengths along the y-axis and heights
perpendicular to their lengths such that their heights are longer,
preferably twice as long, and more preferably about three times as
long as their respective lengths along the y-axis. As shown in
FIGS. 2 and 3 in certain exemplary implementations, the blades
89a-89g have varying thicknesses in a direction perpendicular to
their lengths and heights. In FIGS. 2-3 the blade thicknesses are
oriented along the x-axis. In addition, the thicknesses of blades
89a-89g taper when moving away from shaft or elongated member 88.
In FIGS. 2 and 3, the thickness dimension of the blades is oriented
parallel to the x-axis and tapers when moving in a negative
(downward) direction along the build (z) axis.
[0051] Because solidifiable pastes of the type described herein
will not generally flow due to the force of gravity alone, the
traversal of a spreader can cause volumes of solidifiable paste to
become trapped between the spreader 86 and one of the inner frame
walls 76a or 76b of the solidifiable paste container 48, thereby
depleting the volume of paste available for forming subsequent
object layers. The spreader 86 of FIGS. 2 and 3 is configured to
reduce the amount of such trapped pastes. Blades 89a-89g are spaced
apart from another along the y-axis direction so that each pair of
adjacent blades is separated by a gap along the y-axis. As a result
of this configuration, paste located in the gaps will not be spread
across the container 48. This configuration may be used to impart a
textured profile on the exposed surface of the solidifiable paste,
with the region of the paste contacted by the blades being formed
into a series of troughs or valleys that are separated by peaks. In
addition, the blades 89a-89g are spaced apart from the container
walls 76c and 76d. As shown in FIG. 3, blade 89a is spaced apart by
a distance .DELTA.y.sub.1 from wall 76d and blade 89g is spaced
apart by a distance .DELTA.y.sub.2 from wall 76c. The distances
.DELTA.y.sub.1 and .DELTA.y.sub.2 may be the same or different. In
addition, the inter-blade gap distances may be the same or
different. The inter-blade y-axis gaps in FIG. 3 are shown as
extending along the entire heights (which are along the z-axis in
FIGS. 2 and 3) of blades 89a-89g. However, the gaps could be
configured differently. In certain examples, the y-axis gaps are
present only along a portion of the heights of the blades 89a-89g
and are spaced apart from the spreader shaft or elongated member 88
along an axis defined by the blade heights (i.e., along the z-axis
when the blades 89a-89g are in the rotational orientation of FIG.
2).
[0052] Spreader motor 92 is provided and may be selectively
energized and de-energized to selectively move the spreader 86
along the x-axis. To facilitate x-axis movement, a carriage 90 is
provided and is connected to spreader shaft or elongated member 88.
Spreader motor 92 is preferably operatively connected to a pinion
gear (not shown) that engages a rack gear 100 which extends along
the x-axis. Rack gear 100 is supported by supports 96a and 96b
which are spaced apart from one another along the x-axis and
attached to the top surface 51 of housing 54 (FIG. 1). In FIGS. 2
and 3, only a portion of the rack gear supports 96a and 96b are
shown and their connection to housing 54 is not visible.
[0053] A carriage guide 98 is also provided and extends along the
x-axis. Carriage guide 98 is spaced apart from the rack gear 100
along the build (z) axis. Carriage 90 includes two openings that
face along the x-axis with bushings (not shown in FIGS. 2-3)
mounted therein, and the rack gear 100 and carriage guide 98 each
engage a respective one of the bushings. When spreader motor 92 is
energized, the pinion gear (not shown) rotates about an axis of
rotation parallel to the y-axis. The engagement of the pinion gear
teeth with complementary rack gear 100 teeth, causes the carriage
90 to move along the rack gear 100 and along the x-axis. When the
pinion gear rotates in a first direction about its axis of
rotation, the carriage 90 moves in the positive x-axis direction,
and when the pinion gear rotates in a second direction about its
axis of rotation, the carriage 90 moves in the negative x-axis
direction.
[0054] In certain examples, spreader 86 is pivotable about a pivot
axis that is parallel to the y-axis. In the example of FIGS. 2 and
3, shaft or elongated member 88 is rotatable about its longitudinal
axis to pivot paste spreader 86 to a variety of different pivoted
positions. The pivoting action changes the angular orientation
between the height dimension of the blades 89a-89g and the bottom
of the solidifiable paste container 48 (which is defined by the
rigid or semi-rigid, transparent and/or translucent solidification
substrate 52). The pivoting feature is particularly useful when the
system may be used with different solidifiable pastes with
different rheological properties. As shown in FIG. 2, the leading
edges 91a-91g of the blades 89a-89g extend into the interior volume
of the solidifiable paste container 48. The leading blade edges
91a-91g are spaced apart from solidification substrate 52 by a
distance .DELTA.s. Pivoting the blades 89a-89g about the pivot axis
defined by the shaft or elongated member 88 allows for the
adjustment of the distance .DELTA.s. In addition, paste spreader
assembly 84 may be pivotable and configured so that the shaft or
elongated member 88 is adjustable along the build (z) axis to vary
.DELTA.s. In general, it is preferable to reduce .DELTA.s for
relatively higher viscosity solidifiable pastes as compared to
relatively lower viscosity solidifiable pastes because higher
viscosity pastes will tend to striate when traversing the spreader
86 along the x-axis, with the portion of the solidifiable paste
lying beneath (z-axis) the leading blade edges 91a-91g tending to
remain stationary as the blades 89a-89g spread the paste that lies
above (z-axis) the leading edges 91a-91g.
[0055] Certain solidifiable pastes may have a tendency to form
localized aggregations or clumps of material and/or to form
bubbles. Such phenomena are undesirable because they ultimately
reduce the ability to provide a homogeneous layer of solidifiable
paste between the exposed object surface 64 (FIG. 1) and the
solidification substrate 52. Thus, in certain examples, including
that of FIGS. 2 and 3, the paste spreader assembly 84 includes a
vibrator 94. The vibrator 94 comprises a motor and coupling
connected to shaft or elongated member 88 which move the shaft or
elongated member 88 along the build (z) axis relative to carriage
90, supports 96a and 96b, rack gear 100, carriage guide 98, and the
solidifiable paste container 48. The vibration of spreader 86
causes blades 89a-89g to vibrate along the build (z) axis and
creates localized forces to break up bubbles or agglomerated
sections of paste. In general, the amplitude and/or frequency of
vibration are selected to eliminate any air bubbles formed during a
paste spreading operation. In certain examples, the amplitude
and/or frequency of vibration are selected to create a textured
exposed surface of solidifiable material (e.g., peaks and valleys
or "static waves") so that the pressure exerted by the previously
formed object surface 64 on the exposed surface of solidifiable
paste creates a substantially flat level of solidifiable paste at
the interface between the exposed object surface 64 and the exposed
solidifiable paste surface. In certain preferred examples, the
amplitude of vibration is at least about 1.5 times, more preferably
at least about 1.7 times, and still more preferably at least about
2.0 times the desired layer thickness .DELTA.z of the solidified
object layers. At the same time, the amplitude of vibration is
preferably no more than about 6.0 times, more preferably no more
than about 5.5 times, and still more preferably no more than about
5.0 times the desired layer thickness .DELTA.z. In general, the
vibrational frequency is dependent on and increases with the speed
of traversal of the spreader 86 in a direction perpendicular to the
length of the spreader 86 (i.e., along the x-axis in FIGS.
2-3).
[0056] An exemplary method of making a three-dimensional object
from a solidifiable paste will now be described. In accordance with
the method, a solidifiable paste container such as container 48 is
provided which includes an open top, a closed bottom, and which
contains a solidifiable paste. In the system of FIGS. 2 and 3, the
closed bottom of the solidifiable paste container 48 is defined by
solidification substrate 52, or in the case of certain containers
with films, the closed bottom is defined by solidification
substrate 52 and a film that overlays or is coated on the
solidification substrate 52 (see film 55 overlaying substrate 52 in
FIG. 1). The solidifiable paste container 48 contains a
solidifiable paste with an upward (z-axis) facing exposed surface.
An exposed object surface such surface 64 of FIG. 1 is spaced apart
from the solidification substrate 52 by a desired layer thickness
.DELTA.z. Solidification energy is supplied in a solidification
energy pattern defined by object data representative of the
three-dimensional object to solidify a thickness of the
solidifiable paste lying between exposed object surface 64 and
solidification substrate 52, thereby forming a new section of the
three-dimensional object 59. The exposed surface 64 of the newly
formed object section is then moved along the build (z) axis away
from the solidification substrate 52. Any regions in the
solidifiable paste which have been depleted due to the
solidification process are replenished with a portion of the volume
of the solidifiable paste in the solidifiable paste container 48
(preferably without adding any fresh solidifiable paste) so a
homogeneous section of solidifiable paste with a sufficient
cross-sectional area in the x-y plane and the desired layer
thickness .DELTA.z is available for solidifying the next object
layer. The process is repeated until the object is complete. Fresh
paste may be added periodically. However, in preferred examples,
the replenishment of deplete paste occurs at least several times
during the building of an object without adding fresh solidifiable
paste to the solidifiable paste container. As discussed previously,
in certain preferred implementations of the method, the regions of
depleted paste are only replenished if the x-y area of the object
layer that has just been formed intersects or overlaps with the x-y
area of the next layer to be formed. In certain examples, a program
stored in a controller that outputs a signal to energize or
de-energize the spreader motor 90 will compare the x-y area of the
object data for the next layer to be formed and the one that was
just formed and determine whether the x-y areas intersect or
overlap. If there is no intersection or overlap, the controller
will not energize the spreader motor 90 and may instead set a
variable value (e.g., the value of a flag). That variable value may
then be supplied to a controller that operates the build platform
motor (not shown) and used by a program stored in the build
platform controller to determine when to move the build platform 44
so that the next layer can be formed. If paste spreading is not
occurring, the build platform 44 need only be moved upward along
the build (z) axis by .DELTA.z (the desired layer thickness).
Instead of using separate controllers to operate the spreader motor
90 and the build platform motor (not shown), a single controller
with suitable outputs to each motor may be provided.
[0057] Another exemplary method of making a three-dimensional
object from a solidifiable paste is described by the flow chart of
FIG. 11. In accordance with the method, a build platform is
provided and is moved downward along the build (z) axis until the
exposed object surface 64 (FIG. 1) is spaced apart from the bottom
of the container by a desired layer thickness, .DELTA.z (step
1010). Solidification energy is supplied by a pattern generator, an
example of which is the linear solidification device 42 shown in
FIG. 1. The solidification energy is projected through the closed
bottom of the solidifiable paste container, which in the example of
FIGS. 2 and 3 is the rigid or semi-rigid, transparent and/or
translucent solidification substrate 52, and into the thickness of
solidifiable paste located between the exposed object surface 64
and the substrate 52. The pattern of the supplied solidification
energy corresponds to object data representative of the
three-dimensional object and causes a corresponding portion of the
solidifiable paste located between the exposed object surface 64
and the substrate 52 to solidify (step 1012).
[0058] In step 1014 the build platform motor (not shown) is
energized to move the build platform holder support 46 in the
positive build (z) axis direction (i.e., upward) away from the
solidification substrate 52 (step 1014) by a distance that is
sufficient to provide a build (z) axis clearance of at least
.DELTA.h between the exposed surface 64 (FIG. 1) of the
three-dimensional object 59 and the paste spreader assembly 84 so
that the spreader 86 can move along the x-axis without colliding
with the three-dimensional object 59. In a preferred example, a
controller is provided which outputs a signal to move the build
platform 44 in the positive build (z) axis distance sufficient to
provide a clearance of at least .DELTA.h before outputting a signal
to energize the paste spreader motor 92. In certain examples, one
or more limit switches may be provided along the build platform
elevator 58 to determine when the build platform 44 has reached a
build (z) axis height at which there is a clearance of at least
.DELTA.h. A controller operatively connected to the spreader motor
92 may receive a signal from the one or more limit switches and
execute a program stored in the controller memory. The program may
include instructions for selectively activating the spreader motor
92 when the limit switch signal indicates that the build platform
has been elevated to define a clearance of at least .DELTA.h. In
addition, the program may receive data indicative of the number of
object layers and the thickness of the object layers to adjust the
value of .DELTA.h stored in the controller memory as the object
grows in the negative build (z) axis direction so that the build
platform 44 is elevated to a distance that accounts for the length
of the object 59 along the build (z) axis.
[0059] In step 1016 the spreader 86 is positioned with its leading
edge (i.e., the edge spaced apart from shaft or elongated member
88) beneath the exposed, upward (z-axis) facing surface of the
solidifiable paste in the solidifiable paste container 48. In the
case of FIGS. 2 and 3, step 1016 involves positioning spreader 86
so that the blade leading edges 91a-91g are beneath the exposed
surface of solidifiable paste. In step 1018 the spreader 86 is
moved relative to the solidifiable paste container 48 and/or the
solidifiable paste container 48 is moved relative to the spreader
86. In the example of FIGS. 2 and 3, step 1018 is carried out by
energizing the spreader motor 92 to rotate the pinion gear (not
shown) engaged with rack gear 100 and traverse the carriage 90
along the lengths of rack gear 100 and carriage guide 98 along the
x-axis. However, other configurations may be used to perform step
1016. For example, the solidifiable paste container 48 may be
configured to move along the x-axis relative to the spreader 86
while the spreader 86 remains stationary. In certain examples, step
1016 may further comprise pivoting the spreader blades 89a-89g
about the pivot axis defined by shaft or elongated member 88.
[0060] In step 1020, a determination is made as to whether the last
layer of three-dimensional object 59 has been formed. If it has,
the method ends. Otherwise, control returns to step 1010 to form
the next layer of the three-dimensional object 59. As discussed
previously, in certain preferred implementations of the method of
FIG. 11, steps 1014-1018 are only carried out if the x-y area of
the object layer that has just been formed intersects or overlaps
with the x-y area of the next layer to be formed. In certain
examples, a program stored in a controller that outputs a signal to
energize or de-energize the spreader motor 90 will compare the x-y
area of the object data for the next layer to be formed and the one
that was just formed and determine whether the x-y areas intersect
or overlap. If there is no intersection or overlap, the controller
will not energize the spreader motor 90 and may instead set a
variable value (e.g., the value of a flag). That variable value may
then be supplied to a controller that operates the build platform
motor (not shown) and used by a program stored in the build
platform controller to determine when to move the build platform 44
so that the next layer can be formed. In the case where a current
layer does not intersect or overlap the previous layer in the x-y
plane, the method of FIG. 11 would proceed from step 1012 to step
1020, bypassing steps 1014-1018. Instead of using separate
controllers to operate the spreader motor 90 and the build platform
motor (not shown), a single controller with suitable outputs to
each motor may be provided.
[0061] With certain spreader designs, carrying out step 1018 may
cause an undesirably large volume of solidifiable paste to become
trapped between the spreader 86 and inner container wall 76a or 76b
(depending on the direction of the spreader's traversal along the
x-axis). Due to its viscosity, the trapped solidifiable paste may
limit the x-axis movement of the spreader 86 to an end-of-travel
x-axis location where the spreader 86 is spaced apart from the
container wall 76a or 76b towards which it is moving. If such
trapping occurs each time the spreader 86 is traversed, it can
cause an accumulation of paste proximate the walls 76a and 76b. The
accumulated solidifiable paste becomes effectively unusable for
forming layers of the three-dimensional object 59. Thus, in certain
modified versions of the method of FIG. 11, the spreader 86 will be
lifted out of the solidifiable paste (along the build (z) axis) and
moved along the x-axis to a location proximate one of the walls 76a
and 76b. The leading edge of the spreader 86 will then be
reinserted into the solidifiable paste at the new x-axis location
and traversed away from the proximate wall 76a or 76b, thereby
making the previously trapped paste available for forming the
three-dimensional object.
[0062] FIGS. 2 and 3 depict a paste spreader assembly 84 that is
configured to allow the spreader 86 to be moved out of the
solidifiable paste along the build (z) axis and reinserted
proximate one of the inner solidifiable paste container walls 76a
and 76b. In FIG. 2 two pivoted orientations of the spreader blades
89a-89g are shown in phantom. In one pivoted orientation, the
height dimension of the blades 89a-89g extends in one direction
along the x-axis, and in the other pivoted orientation, the height
dimension of the blades 89a-89g extends in another direction along
the x-axis. With the blades 89a-89g thusly pivoted, the carriage 90
can be translated along the x-axis to locations between walls 76a
and 76b and any trapped paste near the walls. The blades 89a-89g
may then be pivoted downward so their leading edges 91a-91g extend
into the trapped paste. Operation of the spreader motor 92 then
traverses the carriage 90 and the spreader blades 89a-89g to spread
the trapped paste in a direction away from which ever wall 76a or
76b against which the paste was initially trapped. In certain
examples, a motor may be provided and operatively connected to the
paste spreader 86 to pivot the paste spreader 86 and/or elevate its
build (z) axis position to automatically lift the paste spreader 86
out of the solidifiable paste, after which motor 92 traverses the
paste spreader 86 along the x-axis proximate the closest inner
container wall 76a and 76b. The controller may then activate the
pivoting motor to pivot the paste spreader and lower it back into
the solidifiable paste so that a spreading operation may begin.
[0063] Referring to FIGS. 4 and 5, a second exemplary apparatus for
making a three-dimensional object from a solidifiable paste is
depicted. As with the system of FIGS. 2 and 3, housing 54 and
linear solidification device 42 (or another pattern generator)
would be used but are not shown. The build platform assembly and
elevator 58 are configured and operate in the manner described
previously with respect to FIGS. 2 and 3.
[0064] In the system of FIGS. 4 and 5, the solidifiable paste
container 116 has a circular profile when viewed along the build
(z) axis, as best seen in FIG. 4. The solidifiable paste container
116 comprises a vertical wall 120 with a height along the build (z)
axis and a radially outward extending flange 118. A radially
extending inward flange (not shown in FIGS. 3 and 4) is also
provided, and a rigid or semi-rigid, transparent and/or translucent
solidification substrate 122 is positioned in abutting engagement
with the radially-extending inward flange and may be attached
thereto by suitable means of attachment, including adhesives or
mechanical fasteners. The solidifiable paste container 116 is
mounted to a rotating platform 124 that is rotatably attached to
the top surface 51 of the housing 54 (FIG. 1) to rotate the
solidifiable paste container. The rotating platform 124 is
rotatable about an axis of rotation parallel to the build (z) axis.
Other than the circular geometry, solidifiable paste container 116
may be configured similarly to the other solidifiable paste
containers described previously.
[0065] Paste spreader 110 comprises a shaft or elongated member 112
that has a length along the x-axis. However, in other examples,
shaft or elongated member 112 may extend along the y-axis. In
certain examples, the shaft or elongated member 112 may be
positioned to intersect the center axis of the solidifiable paste
container 116 about which the container 116 rotates. In other
examples, and as shown in FIG. 4, the paste spreader 110 is offset
from the center axis of the solidifiable paste container 116. Paste
spreader 110 is oriented to divide the area of the solidifiable
paste container 116 that is perpendicular to the build (z) axis
into first x-y area 117a and second x-y area 117b. The build
platform 44 is movable along the build (z) axis and positioned in
first x-y area 117a during an object building operation. In
accordance with certain examples of apparatuses for making
three-dimensional objects from solidifiable paste, and as
illustrated by the exemplary apparatus of FIGS. 4 and 5, a paste
spreading operation may be carried out by rotating the paste
spreader 110 relative to the solidifiable paste container 116 or
vice-versa. In the example of FIGS. 4 and 5, during a paste
spreading operation the paste spreader 110 remains stationary and
the solidifiable paste container 116 rotates about the center axis
of the container 116. Paste spreader 110 comprises a plurality of
blades 114a-114l having widths along the x-axis and heights
extending perpendicularly to the length of shaft or elongated
member 112 and the x-axis. In the example of FIGS. 4 and 5, the
blades 114a-114l are oriented so that each blade 114a-114l is
spaced apart from its neighbor or neighbors by an x-axis gap. In
addition, the outermost blades 114a and 114l are spaced apart from
the inner surface of the solidifiable paste container vertical wall
120 by a gap 4.x. As with the example of FIGS. 2 and 3, the
inter-blade gaps and the gaps between the blades and the container
walls reduce the amount of solidifiable paste that is trapped
against the container wall during a paste spreading operation. The
inter-blade x-axis gaps in FIG. 5 are shown as extending along the
entire heights (which are along the z-axis in FIG. 5) of blades
114a-114l. However, the gaps could be configured differently. In
certain examples, the x-axis gaps are present only along a portion
of the heights of the blades 114a-114l and are spaced apart from
the spreader shaft or elongated member 110 along an axis defined by
the blade heights (i.e., along the z-axis when the blades 114a-114l
are in the orientation of FIG. 5).
[0066] Spreader shaft or elongated member 112 is connected to a
carriage 118 that is attached to a vertical support 119 mounted on
the top surface 51 of housing 54 (FIG. 1). The carriage 118 can be
selectively moved and secured to different positions along the
build (z) axis to change the distance .DELTA.s between the leading
edges 115a-115l of the blades 114a-114l and the solidification
substrate 122. As with the example of FIGS. 2 and 3, it is
generally preferable to use lower values of .DELTA.s for
solidifiable pastes with relatively higher viscosities and higher
values of .DELTA.s for pastes with relatively lower
viscosities.
[0067] Solidifiable paste container motor 114 (FIG. 4) is provided
to rotate solidifiable paste container 116 in the x-y plane
relative to paste spreader 110. Rotating platform 124 is provided
with a plurality of vertical gear teeth arranged around its
circumference, each gear tooth having a length along the build (z)
axis direction. Energizing motor 114 causes complementary teeth of
a motor gear (not shown) to engage the gear teeth of rotating
platform 124 so that rotation of the motor gear causes the rotating
platform 124 to rotate in the x-y plane about the center axis of
the solidifiable paste container 116. In certain examples, a
controller is provided which selectively outputs a signal to
solidifiable paste container motor 114 to cause it to rotate when a
paste spreading operation is desired. In certain examples, the
output of the signal to the motor 114 is determined by one or more
programs stored in the controller memory and executed by the
controller processor. As with the example of FIGS. 2-3, limit
switches may be provided and connected to provide limit switch
signals to the controller. A controller program may then use the
limit switch signals to determine when to begin a paste spreading
operation by outputting a signal to the motor 114. Signals from the
limit switches may also be used by a controller that outputs a
signal to a build platform motor (not shown) in accordance with a
program stored in the controller memory to move the build platform
44 to the desired build (z) axis location once a paste spreading
operation is complete. One or more limit switches may also be
provided on the build platform elevator 58, and signals from the
limit switches may be provided to spreader motor 114 to selectively
energize the spreader motor 114 and begin a paste spreading
operation once the build platform 44 is at a build (z) axis
position that provides a sufficient clearance between the exposed
object surface 64 and the solidifiable paste as the paste is being
spread. In certain examples, a paste spreading operation may be
carried out by rotating the solidifiable paste container 120
relative to the spreader 110 or vice-versa following the
solidification of each layer. However, in other examples, it may
not be necessary to perform a paste spreading operation if the x-y
region of solidifiable paste that is used to form one layer is
distinct and non-overlapping with the x-y region of solidifiable
paste used to form an adjacent layer because the formation of one
layer will not deplete paste from the x-y region used to form the
adjacent layer. Thus, in some preferred examples, a paste spreading
operation is carried out only when the x-y area of the next object
layer to be formed intersects or overlaps with the x-y area of the
previously formed layer.
[0068] Referring to FIG. 13 a method of using the apparatus of
FIGS. 4 and 5 to make a three-dimensional object from a
solidifiable paste is described. In accordance with the method, a
circular solidifiable paste container 116 is provided with a paste
spreader 110 that is aligned with the container 116 so as to extend
through a portion of the area in which the interior volume of the
container 116 lies (step 1034). In the example of FIGS. 4 and 5,
the paste spreader 110 is offset from the central axis of the
solidifiable paste container 116 (i.e., the axis that extends
through the center of the circular cross-section of the
solidifiable paste container when viewed in a direction along the
build (z) axis). In step 1036, the leading edge of the paste
spreader 110 (which comprises leading edges 115a to 115l in the
case of paste spreader 110) is extended beneath the exposed, upward
facing surface of solidifiable paste (not shown) contained in
solidifiable paste container 116 to define a distance of .DELTA.s
between the leading edges 115a to 115l and the rigid or semi-rigid,
transparent and/or translucent solidification substrate 122.
[0069] The build platform motor (not shown) is energized by a
controller (not shown) to cause the build platform 44 to move
downward along the build (z) axis until the exposed surface 64
(FIG. 1) of the last formed object layer is spaced apart from the
solidification substrate 122 by a desired layer thickness .DELTA.z
(Step 1038). In step 1040 solidification energy is supplied by
linear solidification device 42 (FIG. 1) or whatever pattern
generator is used to solidify a portion of the solidifiable
material in a pattern corresponding to the pattern of the supplied
solidification energy.
[0070] The build platform 44 is raised along the build (z) axis by
a distance sufficient to provide a clearance of at least .DELTA.h
between the exposed object surface 64 and the surface of the
solidifiable paste. In the apparatus of FIGS. 4 and 5, the paste
spreader 110 remains stationary during paste spreading operations
and does not traverse the x-y area occupied by the build platform
44. Thus, unlike the apparatus of FIGS. 2 and 3, collisions between
the object 59 and the paste spreader 110 are not of concern.
However, it may still be necessary to elevate the build platform by
a distance .DELTA.h that is sufficient to ensure that during the
spreading operation, unsolidified paste will not contact the object
59 (FIG. 1) to minimize the likelihood that the moving paste will
damage object 59.
[0071] In step 1044, the paste spreader 110 and container 116 are
rotated relative to one another, either by rotating either or both
of the paste spreader 110 and the container 116. In the example of
FIGS. 4 and 5, the solidifiable paste container 116 rotates, and
the paste spreader 110 remains stationary. In certain examples,
during step 1044 vibrator 121 (FIG. 5) is operated to quickly
traverse paste spreader 110 up and down by a short distance along
the build (z) axis as the solidifiable paste container 116 rotates.
The use of vibrator 121 helps break up bubbles and agglomerations
of solidifiable paste. In general, the amplitude and/or frequency
of vibration are selected to eliminate any air bubbles formed
during a paste spreading operation. In certain examples, the
amplitude and/or frequency of vibration are selected to create a
textured exposed surface of solidifiable material (e.g., peaks and
valleys or "static waves") to that the pressure exerted by the
previously formed object surface 64 on the exposed surface of
solidifiable paste creates a substantially flat level of
solidifiable paste at the interface between the exposed object
surface 64 and the exposed solidifiable paste surface. In certain
preferred examples, the amplitude of vibration is at least about
1.5 times, more preferably at least about 1.7 times, and still more
preferably at least about 2.0 times the desired layer thickness
.DELTA.z. At the same time, the amplitude of vibration is
preferably no more than about 6.0 times, more preferably no more
than about 5.5 times, and still more preferably no more than about
5.0 times the desired layer thickness .DELTA.z. In general, the
vibrational frequency is dependent on and increases with the
relative speed of rotation of the solidifiable paste container 120
and the paste spreader 110.
[0072] A determination is then made as to whether the last layer of
the solidified object 59 (FIG. 1) has been reached (step 1046). If
it has, the process ends. Otherwise, control transfers to step
1038, and steps 1038-1044 are repeated. As discussed previously, in
certain preferred implementations of the method of FIG. 13, steps
1040-1044 are only carried out if the x-y area of the object layer
that has just been formed intersects or overlaps with the x-y area
of the next layer to be formed. In certain examples, a program
stored in a controller that outputs a signal to energize or
de-energize the spreader motor 114 will compare the x-y area of the
object data for the next layer to be formed and the one that was
just formed and determine whether the x-y areas intersect or
overlap. If there is no intersection or overlap, the controller
will not energize the spreader motor 114 and may instead set a
variable value (e.g., the value of a flag). That variable value may
then be supplied to a controller that operates the build platform
motor (not shown) and used by a program stored in the build
platform controller to determine when to move the build platform 44
so that the next layer can be formed. In the case where a current
layer does not intersect or overlap the previous layer in the x-y
plane, the method of FIG. 13 would proceed from step 1040 to step
1046, bypassing steps 1042-1044. Instead of using separate
controllers to operate the spreader motor 90 and the build platform
motor (not shown), a single controller with suitable outputs to
each motor may be provided.
[0073] Referring again to FIG. 4, paste spreader 110 is spaced
apart from the center of the solidifiable paste container 116 to
define a first area 117a and a second area 117b in the x-y plane.
The first area 117a is larger than the second area 117b and defines
the area in the x-y plane in which build platform 44 is located. In
general, as the spacing between the paste spreader 110 and the
center of the solidifiable paste container 116 in the x-y plane
increases, it is preferable to increase the degree of rotation of
the solidifiable paste container 116 relative to the paste spreader
110 (or vice-versa) to ensure that the same internal
cross-sectional area of solidifiable paste container 48 is
traversed by the paste spreader 110 during a paste spreading
operation. In one example, wherein the paste spreader 110 passes
through the center of the solidifiable paste container 116 in the
x-y plane, the solidifiable paste container 116 rotates by 180
degrees (.pi. radians) relative to the paste spreader 110 (either
by rotating the paste spreader 110, the container 116, or both).
However, in the example of FIG. 4 wherein paste spreader 110 is
offset from the center of solidifiable paste container 116 in the
x-y plane, the solidifiable paste container 116 rotates by more
than 180 degrees (.pi. radians) during step 1044 of FIG. 13. In a
preferred example, the angle of rotation of solidifiable paste
container 116 and paste spreader 110 relative to one another is
equal to about 2.pi.-.theta., where .theta. is the angle in radians
defined by a chord that extends along the length of paste spreader
110 to the inner surface of the vertical wall 120 of solidifiable
paste container 116. For example, if .theta. is .pi./2 radians (90
degrees), the angle of rotation of solidifiable paste container 116
and paste spreader 110 relative to one another will preferably be
1.5.pi. (270 degrees).
[0074] As the foregoing paragraph indicates, in certain preferred
examples, during a paste spreading operation, the solidifiable
paste container 120 and the spreader 112 will undergo relative
rotation of no less than 180 degrees (.pi. radians). However, in
certain examples, the extent of the rotation can be less than 180
degrees. In general, the extent of the relative rotation should be
sufficient to ensure that the solidifiable paste lying in the x-y
region occupied by the build platform 44 will be spread. In other
examples, the extent of the relative rotation need only be
sufficient to spread paste lying in the x-y region occupied by the
next object layer to be solidified, which may be only a portion of
the full x-y region occupied by the build platform. Again, where
the x-y region occupied by the next object layer to be formed does
not intersect or overlap the x-y region of the immediately
preceding layer, it may be unnecessary to perform a paste spreading
operation.
[0075] Referring to FIGS. 6-10, another example of an apparatus for
making a three-dimensional object from a solidifiable paste is
depicted. The example of FIGS. 6-10 is similar to the example of
FIGS. 2 and 3 in that the same housing 54 (FIG. 1) and solidifiable
paste container 48 are used, along with a linear solidification
device 42 (FIG. 1) or other pattern generator of the type described
previously). Also, the build platform assembly (i.e., build
platform 44, build platform handles 104a and 104b, build platform
holder 104 and build platform holder support 46) is the same as in
FIGS. 2 and 3. However, the paste spreader assembly 128 is
configured differently. Like the apparatus of FIGS. 2-3, the paste
spreader assembly 128 is depicted as being traversable along the
x-axis to carry out a paste spreading operation but may
alternatively be configured to be traversed along the y-axis to
carry out such operations.
[0076] In FIGS. 6-10 paste spreader assembly 128 comprises first
and second paste spreaders which are exemplified as first and
second blades 130 and 132, each of which has a length along the
y-axis. The first blade 130 and second blade 132 are connected to a
shaft 138 with a handle 140 that projects away from the blades 130
and 132. When viewed along the y-axis, the first blade 130 and
second blade 132 each have heights perpendicular to their
respective lengths which define an angle .alpha. relative to one
another (FIGS. 8A and 8B). The angle .alpha. is preferably at least
about .pi./36 radians (5 degrees), more preferably at least about
.pi./18 radians (10 degrees), and still more preferably at least
about .pi./12 radians (15 degrees). At the same time, the angle
.alpha. is preferably no greater than about 7.pi./36 radians (35
degrees), more preferably no greater than about .pi./6 radians (30
degrees), and still more preferably no greater than about 5.pi./36
radians (25 degrees). In one preferred example, .alpha. is about
.pi./9 radians (20 degrees).
[0077] Paste spreader assembly 128 is rotatable within the x-z
plane to a plurality of rotational positions about an axis of
rotation defined by shaft 138. The paste spreader assembly 128 is
preferably securely repositionable to the plurality of rotational
positions by using a lock. In the example of FIGS. 6-10, the lock
141 comprises a rotating support plate 142 and two spring plungers
146a and 146b. The details of the lock 141 are best seen in FIGS.
8A, 8B, and 10. Rotating support plate 142 comprises two openings
144a and 144b spaced apart along the diameter of rotating support
plate 142 on opposite sides of shaft 138. The spring plungers 146a
and 146b each have a spring and a head that is preferably a rigid
ball. The spring plungers 146a and 146b are attached to the
carriage 90 and are compressible and releasable along the y-axis
direction. When one of the support plate openings 144a and 144b is
aligned with one of the spring plungers 146a and 146b, the spring
will force the plunger head into the aligned opening 144a or 144b
so that the a portion of the head will project part way into the
aligned opening. The projection of the spring head through the
aligned opening 144a or 144b will lock the support plate 142 in a
rotational position corresponding to the location of alignment
between the opening 144a and 144b and the aligned spring plunger
146a and 146b, thereby restraining the rotational movement of the
paste spreader assembly 128 in the x-z plane. The openings 144a and
144b and the heads of spring plungers 146a and 146b are preferably
shaped in a complementary fashion so that a sufficient rotational
force applied to the rotating support plate 142 will cause the
engaged spring plunger head to move along the y-axis and disengage
from the opening with which it was engaged.
[0078] FIG. 8A shows the spreader assembly 128 in a first
rotational position in the x-z plane in which support plate opening
144a is aligned with spring plunger 146a and support plate opening
144b is not aligned with spring plunger 146b. In the depicted
orientation, the rotation of the spreader assembly 128 in the x-z
plane is restrained by the engagement of the head of spring plunger
146a and opening 144a until sufficient rotational force is applied
to rotate the rotating support plate 142 to push the head of spring
plunger 146a in the y-axis direction and out of alignment with
support plate opening 144a.
[0079] FIG. 8B shows the spreader assembly in a second rotational
position in the x-z plane in which spring plunger 146b is aligned
with support plate opening 144b, and spring plunger 146a is not
aligned with support plate opening 144a. In the depicted
orientation, the rotation of the spreader assembly 128 in the x-z
plane is restrained by the engagement of the head of spring plunger
146b and opening 144b until sufficient rotational force is applied
to the rotating support plate 142 to push the head of spring
plunger 146b in the y-axis direction and out of engagement with
support plate opening 144b. In preferred examples, the traversal of
the paste spreader assembly 128 across the solidifiable paste
container along the x-axis does not create a sufficient force
between the solidifiable paste and the blades 130 and 132 to rotate
the support plate 142 with sufficient force to disengage either
spring plunger 146a and 146b from an opening 144a and 144b within
which it is disposed. In general, the springs comprising spring
plungers 146a and 146b are selected with spring constants that are
sufficient to ensure that disengagement does not occur solely due
to contact with the paste during a paste spreading operation and
that disengagement does occur when a container wall 76a, 76b or
hard stop is reached as discussed further below.
[0080] In the rotational positions depicted in FIGS. 8A and 8B,
paste spreader assembly 128 is configured to perform a first
spreading operation (FIG. 8A) by traveling in the positive x-axis
direction (+x) while in a first rotational position and to perform
a second spreading operation (FIG. 8B) by traveling in the negative
x-axis direction (-x) while in a second rotational position. In
certain examples, paste spreader assembly 128 may be rotated to
other rotational positions, such as to perform maintenance
operations. One such rotational position is shown in FIG. 7. In
FIG. 7 paste spreader assembly 128 is rotated such that the leading
blade edges 134 and 139 are spaced apart from the top surface of
the solidifiable paste container 48 (as defined by the inner frame
lip 73) along the build (z) axis. This rotational position is
useful for maintenance operations, for example, pulling the
solidifiable paste container 48 out of the solidifiable paste
container holder 77. Handle 140 allows a user to selectively rotate
the paste spreader assembly 128. By rotating the rotating support
plate 142 sufficiently, support plate opening 144b can be aligned
with the head of plunger 146a to rotate the paste spreader assembly
128 into a position in which both blade leading edges 134 and 139
are spaced apart from the top of the solidifiable paste container.
Alternatively, a user can rotate handle 140 to align support plate
opening 144a with the head of plunger 146b. Thus, in the example of
FIGS. 6-10, the paste spreader assembly 128 can be rotated to two
different rotational orientations in which each of the leading
blade edges 134 and 139 is spaced apart from the top of the
solidifiable paste container 48 along the build (z) axis. The first
such orientation is shown in FIG. 7, in which the first and second
blades 130 and 132 project away from shaft 138 in a first
(positive) direction along the x-axis. In a second rotational
orientation (not shown), the first and second blades 130 and 132
project away from shaft 138 in a second (negative) direction along
the x-axis. To facilitate the addition of paste to solidifiable
paste container 48, blade 130 may be provided with paste refill
window 136, which in the example of FIGS. 6-10 comprises an
elongated opening extending along the y-axis direction. The paste
refill window 136 allows paste to be added to the interior space
defined between the opposing faces of the first blade 130 and
second blade 132. By adding it to the interior space defined
between the opposing faces of the blades 130 and 132, the paste can
be added so as to avoid contact with the leading blade (blade 130
in FIG. 7) during a paste spreading operation, which reduces the
trapping of paste against the inner walls 76a and 76b of the
solidifiable paste container 48 during a paste spreading operation.
Second blade 132 may also be provided with a paste refill
window.
[0081] As illustrated in FIGS. 8A and 8B, in each of the two
depicted spreader assembly 128 rotational orientations, one of the
first blade 130 and second blade 132 is oriented with its height
dimension perpendicular to the bottom 52 of the solidifiable paste
container 48 and with the other blade oriented at an angle equal to
.pi./2-.alpha. radians relative to the bottom 52 of the
solidifiable paste container. In this orientation, the leading edge
of the perpendicular blade defines a spacing (.DELTA.s.sub.1 or
.DELTA.s.sub.4) from the solidifiable paste container bottom 52
along the build (z) axis that is less than the build (z) axis
spacing (.DELTA.s.sub.2 or .DELTA.s.sub.3) of the angled blade's
leading edge from the solidifiable paste container bottom 52. Thus,
in the spreader assembly 128 first rotational orientation of FIG.
8A, the leading edge 139 of second blade 132 is spaced apart from
the solidifiable paste container bottom 52 by a distance
.DELTA.s.sub.1 along the build (z) axis that is less than the build
(z) axis spacing .DELTA.s.sub.2 between the leading edge 134 of
first blade 130 and the solidifiable paste container bottom 52. In
the spreader assembly 128 second rotational orientation of FIG. 8B,
the leading edge 134 of the perpendicular first blade 130 is spaced
apart from the solidifiable paste container bottom 52 by a build
(z) axis distance .DELTA.s.sub.4 that is less than the build (z)
axis spacing .DELTA.s.sub.3 between the leading edge 139 of the
angled second blade 132 and solidifiable paste container bottom 52.
In certain preferred examples, .DELTA.s.sub.1=.DELTA.s.sub.4 and
.DELTA.s.sub.4=.DELTA.s.sub.3. The leading edges 134 and 139 each
have a length along the y-axis and are spaced apart from the shaft
138 by a distance along an axis defined by the height dimensions of
their respective blades 130 and 132. In certain examples, the
leading edges 134 and 139 are smooth along the y-axis direction. In
other examples, the leading edges 134 and 139 are textured along
the y-axis direction. In the example of FIGS. 6-10, the leading
edges 134 and 139 are textured so that they are serrated. As used
herein the term "serrated" refers to a pattern alternating teeth
and notches (or "gullets") such as used in the blade of a saw.
[0082] In certain examples, the use of textured leading spreader
edges can be used to impart an inversely textured profile on the
exposed surface of the solidifiable paste that faces upward along
the build (z) axis. Because of the rheological properties of
solidifiable pastes, it may be difficult to provide a smooth upward
facing surface of paste with which to contact the exposed object
surface 64 (FIG. 1). With low or medium viscosity materials, the
downward pressure applied by the exposed object surface 64 may
create a smooth layer of material. However, that will not
necessarily be the case with the relatively higher viscosity
solidifiable pastes described herein. By providing appropriate
texturing, the exposed surface of the solidifiable paste can be
provided with a variety of alternating peaks and valleys. The
valleys provide a region for receiving displaced material from the
adjacent peaks when pressure is applied to the exposed surface of
the solidifiable paste by the exposed object surface 64 (FIG. 1),
thereby providing a smoother surface of material in contact with
the exposed object surface 64. For example, during a paste
spreading operation, serrated leading edge 134 or serrated leading
edge 139 (depending on the x-axis direction of the paste spreading
operation) will impart a series of alternating peaks and valleys
extending along the x-axis direction. When the exposed object
surface 64 contacts the exposed surface of solidifiable paste, the
pressure applied by the exposed object surface 64 against the paste
will cause paste from the peaks to fill in the valleys, creating an
overall more homogeneous surface and reducing the formation of
voids in the interface between the exposed object surface 64 and
the unsolidified solidifiable paste. In order to apply such
texturing with the serrated leading edges 134 and 139, the trailing
blade is preferably positioned with the notches of its leading edge
positioned at or slightly above the exposed surface of the
solidifiable paste along the build (z) axis and with its teeth
positioned beneath the exposed surface of the solidifiable
paste.
[0083] The paste spreader assembly 128 is traversable in both first
and second directions along the x-axis to carry out paste spreading
operations. Spreader motor 92 comprises a shaft 95 on which pinion
gear 148 (FIG. 10) is mounted. The teeth of pinion gear 148 have
lengths oriented along the y-axis direction and engage rack gear
100. Rack gear 100 is attached to carriage 90 via bushing 145a and
is oriented with its length along the x-axis. A guide 98 is
attached to carriage 90 via bushing 145b. Guide 98 comprises a
generally smooth shaft that is oriented with its length along the
x-axis and which is spaced apart from rack gear 100 along the build
(z) axis direction. The ends of both rack gear 100 and guide 98 are
attached to supports 96a (not visible) and 96b (FIG. 6) which are
attached to the upper surface 51 of housing 54 (FIG. 1). Rotating
support plate 142 is rotatably mounted to carriage 90 via bushing
145c (FIG. 10). Energization of spreader motor 92 causes the pinion
gear 148 to rotate. When it rotates in a first rotational direction
in the x-z plane, the engagement of pinion gear 148 and rack gear
100 causes the pinion gear 148 (and carriage 90) to travel along
the rack gear 100 along a first x-axis direction. When it rotates
in a second rotational direction in the x-z plane, the engagement
of pinion gear 148 and rack gear 100 causes the pinion gear 148
(and carriage 90) to travel along the rack gear 100 along a second
x-axis direction that is opposite the first x-axis direction. As
carriage 90 travels in a direction along the x-axis, the shaft 138,
handle 140, rotating support plate 142 and blades 130 and 132
travel in the same direction along the x-axis. In certain examples,
spreader motor 92 is operatively connected to and receives a signal
that is selectively provided from a controller to energize and
de-energize the spreader motor 92. In one possible configuration, a
limit switch provided on the build platform elevator 58 may be used
to determine when build platform 44 has been safely elevated to a
build (z) axis position at which the paste spreader assembly 128
can be traversed without colliding with the object 59 (FIG. 1) or
the build platform 44. The controller may receive a signal from the
limit switch and process it using a program stored in the
controller memory and executed by the controller processor to
determine when to output a signal to spreader motor 92 to energize
the motor 92. Limit switches may also be provided on or proximate
two the ends of the rack gear 100 and/or the guide 98 to indicate
when the carriage 90 has reached the end of travel in the positive
or negative x-axis directions, and the controller may use those
limit switch signals to determine when a spreading operation is
complete and when to de-energize the spreader motor 92. The same
controller or a different controller may also receive signals
provided by limit switches located along or proximate to the rack
gear 100 and/or guide 98 to when to bring the build platform 44
downward along the build (z) axis to solidify another layer of
solidifiable paste.
[0084] As best seen in FIG. 6, paste spreader assembly 128 is
preferably positioned relative to solidifiable paste container 48
such that the leading edges 134 and 139 of the first blade 130 and
second blade 132 are located beneath the top of the solidifiable
paste container (i.e., beneath the upward (z-axis) facing surface
of the lip 73 of the inner frame 72) and spaced apart from the
bottom 52 of the solidifiable paste container 48 by respective
distances .DELTA.s.sub.1 and .DELTA.s.sub.4 along the build (z)
axis. In the figures, the paste is not shown in the solidifiable
paste container 48.
[0085] In certain preferred modes of operation, during a paste
spreading operation one of the first blade 130 and the second blade
132 will be spaced apart from the other of the first blade 130 and
the second blade 132 in the direction of travel of paste spreader
assembly 128 along the x-axis. The blade that is positioned farther
along the direction of travel during a paste spreading operation
may be referred to as the "leading blade," while the blade that is
positioned farther behind along the direction of travel may be
referred to as the "trailing blade." In a preferred mode of
operation, during a paste spreading operation the leading edge of
the trailing blade is positioned beneath the exposed upward facing
surface of the solidifiable paste along the build (z) axis, and the
leading edge of the leading blade is spaced above the exposed
surface of the solidifiable paste along the build (z) axis. Thus,
in this preferred mode of operation, during a spreading operation,
the spreading is carried out by the trailing blade only.
[0086] As compared to a single blade spreader assembly, the dual
blade spreader assembly 128 of FIGS. 6-10 advantageously reduces
the amount of solidifiable paste that is trapped against the inner
solidifiable container walls 76a or 76b during a paste spreading
operation. If only one of the first blade 130 or the second blade
132 were provided, as the blade approached either of the inner
container walls 76a or 76b, the blade would trap a volume of
solidifiable paste between the blade and the wall due to the
rheological properties of the solidifiable paste. In order to
recover the trapped paste for use in subsequent object
solidification operations, the blade would have to be lifted above
the exposed surface of solidifiable paste along the build (z) axis
and reinserted into the paste immediately proximate the wall 76a or
76b. In one exemplary mode of operation, as best seen in FIGS. 8A
and 8B, the apparatus of FIGS. 6-10 avoids the necessity of lifting
the blades 130 and 132 in this manner.
[0087] Referring to FIG. 8A, the paste spreader assembly 128 is
shown near the end of a left to right first paste spreading
operation along the positive x-axis direction in which the leading
edge 134 of the leading blade 130 approaches the inner wall 76b of
inner frame 72 of the solidifiable paste container 48. During the
paste spreading operation shown in FIG. 8A, the first blade 130
acts as the leading blade and the second blade 132 acts as the
trailing blade. In this configuration, the leading edge 134 of the
first blade 130 is preferably positioned above the exposed surface
of the solidifiable paste (not shown) so as to reduce the amount of
paste that is trapped between the first blade 130 and the inner
wall 76b of solidifiable paste container 48. Once the first blade
130 begins to engage the inner wall 76b, support plate 142 applies
a force against the head of spring plunger 146a that is sufficient
to depress the head of spring plunger 146a in the y-axis direction,
thereby allowing the support plate 142 to rotate in the clock-wise
direction. As the support plate 142 rotates, opening 144b will
eventually come into alignment with the head of spring plunger
146b, at which point the spring force within the spring plunger
146b will force the head of spring plunger 146b to move along the
y-axis into opening 144b. At this point, first blade 130 has been
rotated so that its height dimension is perpendicular to the bottom
52 of the solidifiable paste container 48. At the same time, the
second blade 132 has been rotated with its height dimension
oriented at an angle of 2.pi.-.alpha. relative to the bottom 52 of
the solidifiable paste container 48. With the paste spreader
assembly 128 now releasably secured in the second rotational
position in the x-z plane, the spreader assembly is ready to begin
a second paste spreading operation in which the paste spreader
assembly 128 travels from right to left in the negative x-axis
direction. In this second paste spreading operation, the second
blade 132 will act as the leading blade and will remain spaced
apart from the first blade 130 in the negative x-axis direction as
the paste spreader assembly 128 travels in the negative x-axis
direction. As indicated previously, in a preferred mode of
operation, the leading edge 139 of the second blade 132 will be
spaced above the exposed surface of the solidifiable paste along
the build (z) axis, and the leading edge 134 of the first blade 130
will be positioned beneath the exposed surface of the solidifiable
paste along the build (z) axis. Once the second blade 132 reaches
and engages inner container wall 76a, the engagement will cause the
rotating support plate 142 to apply a force to the head of spring
plunger 146a, thereby depressing it along the y-axis and rotating
the rotating support 142 plate in the counter clockwise direction
in the x-z plane until the head of spring plunger 146a engages the
opening 144a in support plate 142 to lock the support plate 142
into the first rotational position shown in FIG. 8A.
[0088] As depicted in FIGS. 6-10, the rotation of the paste
spreader assembly 128 in the x-z plane occurs due to the engagement
of whichever blade 130 and 132 is the leading blade and one of the
container walls 76a or 76b. However, other mechanisms may be
provided to rotate the spreader assembly 128. In one example, one
or more "hard stops" are provided in the solidifiable paste
container. In one implementation, one or two upside-down L-shaped
members may be provided on each side of the solidifiable paste
container 74 and spaced apart along the direction of travel of the
spreader assembly 128 (i.e., spaced apart along the x-axis in the
apparatus of FIGS. 6-10). The hard stops would be positioned with
one of the sides of the "L's" extending along a direction
perpendicular to the direction of travel of the paste spreader
assembly 128 (i.e., along the y-axis in the apparatus of FIGS.
6-10) and positioned so engage the leading blade of the paste
spreader assembly 128 proximate the container walls 76a and 76b. In
one example, pairs of upside-down L members are spaced apart along
the x-axis, and the two members of each pair are spaced apart from
one another along the y-axis with respective portions of each
member projecting inwardly along the y-axis toward the other
member.
[0089] In certain examples, the use of such hard stops beneficially
avoids relying on the collision of the leading blade and the
container walls 76a and 76b, which may reduce wear on and better
preserve the integrity of container 74. As an alternative to
relying on the physical engagement of a leading spreader blade with
a container 74 wall or other hard stop, the paste spreader assembly
may be operatively connected to a motor that adjusts the rotational
orientation of the spreader assembly 128 from that of FIG. 8A to
that of FIG. 8B (and vice-versa) without relying on such physical
engagement. In one example, limit switches may be provided that
determine the location of the paste spreader assembly 128 along the
direction of travel (i.e., the x-axis in FIGS. 6-10), and a
controller may be used to selectively energize a rotational motor
in response to signals received from the limit switches to adjust
the rotational position of the paste spreader assembly 128.
[0090] Referring to FIG. 12, an exemplary method of carrying out
step 1018 of FIG. 11 ("Move spreader relative to solidifiable
material container or vice-versa") using the apparatus of FIGS.
6-10 will now be described. In accordance with the method, in step
1022 the paste spreader assembly 128 is located proximate container
wall 76a or 76b and is provided in a first rotational orientation
with a first spring plunger head projecting through a first support
plate hole. For example, as shown in FIG. 6, paste spreader
assembly 128 starts a paste spreading operation proximate inner
container wall 76a in a first rotational orientation depicted in
FIG. 8A. In the first rotational orientation, the head of spring
plunger 146a is aligned with support plate opening 144a so as to
project partially through the opening 144a and lock the support
plate 142 against rotation, thereby restraining the rotational
movement of a the trailing spreader (second spreader 132) and the
leading spreader (first spreader 130). In step 1024 the paste
spreader assembly 128 is traversed along a first x-axis direction
relative to the build platform 44 and the bottom 52 of the
solidifiable paste container 48 with the trailing blade oriented
perpendicularly to the bottom 52 of the solidifiable paste
container 48 and the leading blade oriented at an angle of
2.pi.-.alpha. relative to the bottom 52 of solidifiable paste
container 48. As with the apparatuses of FIGS. 2-5, in certain
examples, paste spreading operations may be carried out with the
apparatus of FIGS. 6-10 only when the current layer occupies an x-y
region that intersects or overlaps with that of the previously
formed layer. One or more controllers used to operate the build
platform motor (not shown) and the paste spreader motor 90 may be
operated in the manner described with respect to the apparatuses of
FIGS. 2-5 to limit paste spreading operations to those situations
in which the current layer occupies an x-y region that overlaps
with or intersects the x-y region of the immediately preceding
layer.
[0091] As the leading blade of the paste spreader assembly 128
approaches an inner wall (76a or 76b) of the solidifiable paste
container 48, the leading blade engages the inner wall (76a or 76b)
(step 1026). An illustration of the moment before such engagement
is shown in FIG. 8A. The engagement causes the engaged blade to
apply a rotating force to rotating support plate 142. The rotating
force causes the rotating support plate 142 to exert a force
against the head of the spring plunger that is currently engaged
with one of the support plate openings 144a and 144b. In the case
of FIG. 8A, the rotating support plate 142 would exert a force
against the head of spring plunger 146a, causing it to depress the
head of spring plunger 146a along the y-axis and out of engagement
with rotating support plate opening 144a (step 1028). The continued
engagement of the leading blade with the inner wall of the
solidifiable paste container 48 (e.g., the continued engagement of
leading blade 130 with inner container wall 76b in FIG. 8A) rotates
the rotating support plate 142 and the first and second blades 130
and 132 about the axis of rotation defined by shaft 138 (step 1030)
until another support plate opening engages another spring plunger
head (step 1032). In the example of FIGS. 8A and 8B, the continued
engagement of the leading spreader (first spreader 130) and the
inner wall 76b of solidifiable paste container 48 rotates the
rotating support plate 142 in a clockwise direction until opening
144b comes into alignment with the head of spring plunger 146b, at
which point the head of spring plunger 146b engages the opening
144b to lock the rotational position of the rotating support plate
142 into the position shown in FIG. 8B. Thus, steps 1022 to 1032
provide one exemplary way of carrying out step 1018 of FIG. 11.
[0092] As with the example of FIGS. 2-3, in general, in the
apparatus of FIGS. 6-10 it is preferable to space the leading edge
of the trailing blade by a distance .DELTA.s that is closer to the
bottom 52 of the solidifiable paste container 48 for higher
viscosity solidifiable pastes relative to lower viscosity
solidifiable pastes. In one example, the supports 96a (not shown)
and 96b (FIG. 6) may be vertically adjustable to adjust the
distance of the rack gear 100 and guide 98 from the bottom 52 of
the solidifiable paste container to allow for variable build (z)
axis spacing between the leading edges 134 and 139 of blades 130
and 132 in any given rotational position of the rotating support
plate 142. In other examples, the additional support plate holes
and spring plungers may be provided so that the trailing blade can
be angled relative to the bottom 52 of the solidifiable paste
container 48 as a means of varying the build (z) axis spacing
between the trailing blade and the bottom 52 of the solidifiable
paste container 48. In certain examples, the apparatus of FIGS.
6-10 may also be configured for build (z) axis vibration to assist
in breaking up bubbles and/or agglomerations of solidifiable
paste.
[0093] The present invention has been described with reference to
certain exemplary embodiments thereof. However, it will be readily
apparent to those skilled in the art that it is possible to embody
the invention in specific forms other than those of the exemplary
embodiments described above. This may be done without departing
from the spirit of the invention. The exemplary embodiments are
merely illustrative and should not be considered restrictive in any
way. The scope of the invention is defined by the appended claims
and their equivalents, rather than by the preceding
description.
* * * * *